- A serum sample appears grossly lipemic. Which analyte is most likely to be falsely affected by this interference in spectrophotometric assays?
- Creatinine by Jaffe
- Sodium measured by indirect ISE
- Glucose by hexokinase
- Total bilirubin
Correct answer: Sodium measured by indirect ISE
Lipemia displaces the aqueous volume of plasma, causing pseudohyponatremia when sodium is measured by indirect (diluted) ion-selective electrode methods. Direct ISE methods are not affected.
- Which condition is most consistent with a low anion gap?
- Hypoalbuminemia
- Lactic acidosis
- Salicylate poisoning
- Diabetic ketoacidosis
Correct answer: Hypoalbuminemia
Albumin is the major unmeasured anion; hypoalbuminemia decreases the anion gap. Each 1 g/dL drop in albumin lowers the gap by about 2.5 mEq/L.
- A patient's troponin I is elevated and rising over serial draws. This pattern is most specific for which condition?
- Skeletal muscle trauma
- Stable angina
- Chronic kidney disease
- Acute myocardial injury
Correct answer: Acute myocardial injury
A rising and/or falling pattern of cardiac troponin above the 99th percentile indicates acute myocardial injury. Cardiac troponin I is highly specific for myocardium unlike CK-MB.
- Which calculation correctly estimates LDL cholesterol using the Friedewald equation?
- HDL−(triglycerides/2.2)
- Total−HDL−(triglycerides/5)
- Total+HDL−triglycerides
- Total−HDL+(triglycerides/5)
Correct answer: Total−HDL−(triglycerides/5)
The Friedewald equation is LDL=Total cholesterol−HDL−(triglycerides/5) in mg/dL. It is invalid when triglycerides exceed 400 mg/dL.
- A markedly elevated alkaline phosphatase with normal GGT in a growing adolescent most likely originates from which source?
- Liver
- Bone
- Placenta
- Intestine
Correct answer: Bone
Bone isoenzyme elevation is normal in growing children and adolescents due to osteoblastic activity. A normal GGT indicates the elevation is not hepatobiliary in origin.
- Which sample handling error most commonly causes spurious hyperkalemia?
- Centrifuging immediately
- Using a heparinized tube
- Storing serum at 4 degrees C
- Delayed centrifugation with hemolysis
Correct answer: Delayed centrifugation with hemolysis
Potassium is concentrated inside red cells; hemolysis or delayed separation allows leakage into serum, falsely elevating measured potassium. Prompt separation prevents this.
- In the hexokinase method for glucose, which coupled enzyme generates the measured NADPH?
- Lactate dehydrogenase
- Glucose-6-phosphate dehydrogenase
- Glucose oxidase
- Peroxidase
Correct answer: Glucose-6-phosphate dehydrogenase
Hexokinase phosphorylates glucose to glucose-6-phosphate, which G6PD oxidizes while reducing NADP to NADPH. The increase in absorbance at 340 nm is proportional to glucose.
- A patient has elevated total calcium but a normal ionized calcium. The most likely explanation is:
- Primary hyperparathyroidism
- Vitamin D toxicity
- Malignancy
- Increased serum albumin
Correct answer: Increased serum albumin
About half of serum calcium is protein-bound, mainly to albumin. Elevated albumin raises total calcium while the physiologically active ionized fraction remains normal.
- Which finding best distinguishes prerenal azotemia from intrinsic renal failure?
- BUN/creatinine ratio greater than 20:1
- Presence of muddy brown casts
- Low urine specific gravity
- Elevated urine sodium
Correct answer: BUN/creatinine ratio greater than 20:1
Prerenal azotemia shows a disproportionately high BUN relative to creatinine (ratio greater than 20:1) due to enhanced tubular urea reabsorption with preserved tubular function.
- Hemoglobin A1c primarily reflects average glycemic control over what period?
- 6 to 12 months
- 2 to 3 months
- 1 to 2 weeks
- 1 to 2 days
Correct answer: 2 to 3 months
HbA1c reflects nonenzymatic glycation of hemoglobin over the roughly 120-day red cell lifespan, weighted toward the most recent 2 to 3 months.
- Which protein is the best early marker for glomerular damage and microalbuminuria screening in diabetics?
- Albumin
- Bence Jones protein
- Transferrin
- Beta-2 microglobulin
Correct answer: Albumin
Small amounts of albumin in urine (microalbuminuria) are an early indicator of diabetic glomerular damage and are used for screening before overt proteinuria develops.
- An elevated direct (conjugated) bilirubin with elevated alkaline phosphatase and dark urine suggests:
- Hemolytic anemia
- Gilbert syndrome
- Obstructive (post-hepatic) jaundice
- Neonatal physiologic jaundice
Correct answer: Obstructive (post-hepatic) jaundice
Conjugated bilirubin is water soluble and appears in urine; combined with elevated ALP it indicates cholestatic or obstructive jaundice. Hemolysis and Gilbert raise unconjugated bilirubin.
- Which enzyme elevation is most specific for acute pancreatitis when interpreted with clinical findings?
- Alkaline phosphatase
- Amylase alone
- Lipase
- AST
Correct answer: Lipase
Lipase is more specific and remains elevated longer than amylase in acute pancreatitis. Amylase can also rise in salivary disorders and other conditions.
- The reference method for measuring serum sodium and potassium in most automated analyzers is:
- Ion-selective electrode
- Coulometry
- Atomic absorption
- Flame photometry
Correct answer: Ion-selective electrode
Ion-selective electrodes have replaced flame photometry for routine electrolyte measurement. They are faster, safer, and can be direct or indirect.
- A TSH is elevated and free T4 is low. This pattern indicates:
- Euthyroid sick syndrome
- Graves disease
- Primary hypothyroidism
- Secondary hyperthyroidism
Correct answer: Primary hypothyroidism
In primary hypothyroidism the thyroid fails, so free T4 falls and the pituitary increases TSH output. This is the classic compensatory pattern.
- Which is the recommended specimen for blood lactate to avoid spurious elevation?
- Clotted serum tube at room temperature
- EDTA tube
- Sodium fluoride tube collected without tourniquet stasis
- Heparin tube left 2 hours
Correct answer: Sodium fluoride tube collected without tourniquet stasis
Lactate rises in vitro from continued glycolysis; sodium fluoride inhibits glycolysis and collection without prolonged tourniquet stasis prevents false elevation. Prompt processing is also key.
- Which serum electrophoresis pattern is characterized by a sharp homogeneous spike in the gamma region?
- Polyclonal gammopathy
- Nephrotic syndrome
- Monoclonal gammopathy
- Acute inflammation
Correct answer: Monoclonal gammopathy
A monoclonal (M) spike is a discrete, sharp band reflecting a single immunoglobulin clone, characteristic of multiple myeloma or MGUS. Polyclonal increases produce a broad-based elevation.
- The principal buffer system in extracellular fluid is:
- Hemoglobin
- Protein
- Phosphate
- Bicarbonate/carbonic acid
Correct answer: Bicarbonate/carbonic acid
The bicarbonate/carbonic acid system is the most important extracellular buffer because the respiratory and renal systems independently regulate COX2 and bicarbonate.
- A blood gas shows pH 7.30, pCOX2 30, HCOX3 14. This represents:
- Metabolic acidosis with respiratory compensation
- Metabolic alkalosis
- Respiratory alkalosis
- Respiratory acidosis
Correct answer: Metabolic acidosis with respiratory compensation
Low pH with low bicarbonate indicates metabolic acidosis; the low pCOX2 reflects respiratory compensation through hyperventilation.
- Which marker is most useful for monitoring germ cell tumors and is also elevated in pregnancy?
- PSA
- CA-125
- CEA
- Alpha-fetoprotein
Correct answer: Alpha-fetoprotein
Alpha-fetoprotein is a tumor marker for hepatocellular carcinoma and nonseminomatous germ cell tumors and is physiologically elevated in pregnancy and fetal development.
- Which automated red cell index is used to classify anemias by cell size?
Correct answer: MCV
Mean corpuscular volume (MCV) classifies anemias as microcytic, normocytic, or macrocytic. It is calculated from hematocrit and red cell count.
- Howell-Jolly bodies on a peripheral smear are most commonly associated with:
- Vitamin C deficiency
- Lead poisoning
- Iron deficiency
- Asplenia or splenic hypofunction
Correct answer: Asplenia or splenic hypofunction
Howell-Jolly bodies are nuclear DNA remnants normally removed by the spleen. Their presence suggests absent or hypofunctional spleen, as after splenectomy.
- A blood smear shows numerous schistocytes, thrombocytopenia, and elevated LDH. These findings suggest:
- Microangiopathic hemolytic anemia
- Hereditary spherocytosis
- Iron deficiency anemia
- Megaloblastic anemia
Correct answer: Microangiopathic hemolytic anemia
Schistocytes (fragmented RBCs) with thrombocytopenia and elevated LDH indicate mechanical red cell destruction seen in MAHA, such as TTP, HUS, or DIC.
- Which stain is used to demonstrate reticulocytes?
- New methylene blue
- Wright stain
- Prussian blue
- Sudan black B
Correct answer: New methylene blue
New methylene blue is a supravital stain that precipitates residual reticulocyte RNA into a visible reticulum. Reticulocytes appear as polychromatophilic cells on Wright stain.
- Auer rods in the cytoplasm of blasts are diagnostic of which lineage?
- Myeloid
- Erythroid
- Lymphoid
- Megakaryocytic
Correct answer: Myeloid
Auer rods are crystallized azurophilic granules found in myeloblasts and promyelocytes, confirming a myeloid lineage in acute myeloid leukemia.
- The most common cause of microcytic hypochromic anemia worldwide is:
- Sideroblastic anemia
- Iron deficiency
- Anemia of chronic disease
- Thalassemia
Correct answer: Iron deficiency
Iron deficiency is the most prevalent cause of microcytic hypochromic anemia globally, typically with low ferritin and elevated TIBC.
- Which laboratory finding helps distinguish iron deficiency anemia from anemia of chronic disease?
- Serum ferritin low in iron deficiency
- MCV always normal in iron deficiency
- TIBC low in iron deficiency
- Serum iron high in iron deficiency
Correct answer: Serum ferritin low in iron deficiency
Ferritin is low in iron deficiency but normal or elevated in anemia of chronic disease (it is an acute phase reactant). TIBC is high in iron deficiency and low in chronic disease.
- Hypersegmented neutrophils and oval macrocytes are characteristic of:
- Megaloblastic anemia
- Sickle cell disease
- Aplastic anemia
- Iron deficiency
Correct answer: Megaloblastic anemia
Megaloblastic anemia from B12 or folate deficiency causes impaired DNA synthesis, producing oval macrocytes and hypersegmented neutrophils with five or more lobes.
- The Philadelphia chromosome t(9;22) is the hallmark of which disorder?
- Hodgkin lymphoma
- Polycythemia vera
- Chronic myelogenous leukemia
- Acute lymphoblastic leukemia
Correct answer: Chronic myelogenous leukemia
The t(9;22) translocation produces the BCR-ABL1 fusion gene with constitutive tyrosine kinase activity, the defining feature of CML and a target of imatinib therapy.
- Which RBC inclusion contains denatured hemoglobin and is seen in G6PD deficiency after oxidative stress?
- Pappenheimer bodies
- Heinz bodies
- Cabot rings
- Basophilic stippling
Correct answer: Heinz bodies
Heinz bodies are precipitated denatured hemoglobin demonstrated with supravital stains; they form in G6PD deficiency under oxidative stress, producing bite cells.
- The erythrocyte sedimentation rate is most directly increased by elevated levels of:
- Glucose
- Bilirubin
- Fibrinogen
- Albumin
Correct answer: Fibrinogen
Fibrinogen and other acute phase proteins promote rouleaux formation, increasing the rate red cells settle. Thus ESR is a nonspecific marker of inflammation.
- A patient with a markedly elevated WBC count, basophilia, and the full spectrum of granulocyte maturation in the blood most likely has:
- Chronic myelogenous leukemia
- Leukemoid reaction
- Chronic lymphocytic leukemia
- Acute myeloid leukemia
Correct answer: Chronic myelogenous leukemia
CML shows marked leukocytosis with the entire maturation series of granulocytes and frequent basophilia, distinguishing it from acute leukemia which shows a blast predominance.
- Target cells are most characteristically seen in which condition?
- Polycythemia
- Hereditary spherocytosis
- Iron deficiency only
- Liver disease and hemoglobinopathies
Correct answer: Liver disease and hemoglobinopathies
Target cells (codocytes) have excess membrane relative to cytoplasm and appear in liver disease, hemoglobinopathies such as HbC and thalassemia, and post-splenectomy.
- What does a high RDW indicate?
- Increased red cell hemoglobin
- Increased variation in red cell size (anisocytosis)
- Increased white cell count
- Decreased platelet count
Correct answer: Increased variation in red cell size (anisocytosis)
Red cell distribution width quantifies the variation in red cell size. An elevated RDW indicates anisocytosis, useful in distinguishing iron deficiency from thalassemia.
- The principle of the automated impedance method for counting blood cells is based on:
- Enzymatic color change
- Change in electrical resistance as a cell passes through an aperture
- Light scatter from a laser
- Fluorescent labeling
Correct answer: Change in electrical resistance as a cell passes through an aperture
In impedance (Coulter) counting, cells passing through an aperture between electrodes momentarily increase electrical resistance; pulse number equals cell count and pulse size relates to volume.
- Toxic granulation, Dohle bodies, and a left shift are most consistent with:
- Severe bacterial infection or sepsis
- Parasitic infection
- Viral infection
- Allergic reaction
Correct answer: Severe bacterial infection or sepsis
Toxic changes including toxic granulation, Dohle bodies, and a left shift with band neutrophils reflect accelerated neutrophil production in severe bacterial infection or sepsis.
- Sickle cell disease results from a single amino acid substitution at position 6 of the beta-globin chain, replacing glutamic acid with:
- Valine
- Serine
- Glycine
- Lysine
Correct answer: Valine
In hemoglobin S, valine replaces glutamic acid at the sixth position of the beta chain, causing polymerization of deoxygenated hemoglobin and red cell sickling.
- Which cell predominates in the differential of a patient with chronic lymphocytic leukemia, often accompanied by smudge cells?
- Eosinophils
- Mature lymphocytes
- Myeloblasts
- Plasma cells
Correct answer: Mature lymphocytes
CLL is characterized by accumulation of mature-appearing small lymphocytes; the fragile cells rupture during smear preparation, producing smudge (basket) cells.
- Which is the correct anticoagulant tube for a routine CBC?
- Sodium citrate (light blue)
- Heparin (green)
- Sodium fluoride (gray)
- EDTA (lavender)
Correct answer: EDTA (lavender)
EDTA in the lavender-top tube preserves cell morphology and prevents platelet clumping, making it the standard anticoagulant for hematology testing.
- Tear-drop cells (dacrocytes) and a leukoerythroblastic blood picture suggest:
- Myelofibrosis or marrow infiltration
- Iron deficiency
- Hemolytic anemia
- Acute blood loss
Correct answer: Myelofibrosis or marrow infiltration
Dacrocytes with nucleated RBCs and immature granulocytes (leukoerythroblastic picture) indicate marrow stress from fibrosis or infiltration, as in primary myelofibrosis.
- Which group of individuals is the universal red cell donor for ABO?
- A positive
- AB positive
- O negative
- B negative
Correct answer: O negative
Group O has no A or B antigens on red cells, and Rh-negative lacks D antigen, so O negative red cells can be given safely to most recipients in emergencies.
- A patient types as A on forward grouping but the reverse grouping shows agglutination with both A1 and B cells. The most likely explanation is:
- A weak D
- An A subgroup with anti-A1
- A cold autoantibody
- The patient is group O
Correct answer: An A subgroup with anti-A1
An A subgroup such as A2 may produce anti-A1, causing unexpected reverse-grouping agglutination with A1 cells. This is a common ABO discrepancy requiring resolution.
- The direct antiglobulin test (DAT) detects:
- ABO antigens
- Platelet antibodies
- Antibodies or complement already bound to the patient's red cells
- Antibodies in patient serum
Correct answer: Antibodies or complement already bound to the patient's red cells
The DAT detects in vivo coating of red cells with IgG or complement, used to investigate hemolytic transfusion reactions, HDFN, and autoimmune hemolytic anemia.
- Rh immune globulin (RhIG) is given to prevent alloimmunization in which situation?
- Rh-negative mother carrying or delivering an Rh-positive infant
- Rh-positive mother with Rh-negative fetus
- Rh-positive mother carrying Rh-positive infant
- All pregnant women regardless of Rh
Correct answer: Rh-negative mother carrying or delivering an Rh-positive infant
RhIG prevents an Rh-negative mother from forming anti-D after exposure to Rh-positive fetal cells, reducing the risk of hemolytic disease in future pregnancies.
- Which antibody class is most commonly responsible for hemolytic disease of the fetus and newborn because it crosses the placenta?
Correct answer: IgG
Only IgG antibodies cross the placenta. Maternal IgG anti-D and other IgG red cell antibodies can sensitize and destroy fetal red cells.
- The purpose of adding IgG-coated red cells (check cells) to a negative antiglobulin test is to:
- Remove fibrin
- Enhance cold antibody reactions
- Confirm that AHG reagent was added and is active
- Detect weak antigens
Correct answer: Confirm that AHG reagent was added and is active
Check cells (Coombs control cells) are sensitized with IgG; they must agglutinate in a valid negative AHG test, confirming the antiglobulin reagent was added and not neutralized.
- A delayed hemolytic transfusion reaction is most often caused by:
- Volume overload
- An anamnestic antibody response to a previously sensitized antigen such as Kidd
- ABO incompatibility
- Bacterial contamination
Correct answer: An anamnestic antibody response to a previously sensitized antigen such as Kidd
Delayed reactions occur when a previously formed antibody, often anti-Jka in the Kidd system, drops below detectable levels then rapidly rises after re-exposure, causing extravascular hemolysis days later.
- Which component is the treatment of choice to raise fibrinogen in a bleeding patient with hypofibrinogenemia?
- Platelet concentrate
- Cryoprecipitate
- Fresh frozen plasma
- Packed red cells
Correct answer: Cryoprecipitate
Cryoprecipitate is concentrated in fibrinogen, factor VIII, von Willebrand factor, and factor XIII, making it the preferred product for hypofibrinogenemia.
- Most clinically significant red cell alloantibodies react optimally at which temperature?
- 0 degrees C
- 37 degrees C
- 22 degrees C
- 4 degrees C
Correct answer: 37 degrees C
Clinically significant antibodies are usually IgG and react best at body temperature (37 degrees C) and in the antiglobulin phase. Cold-reactive IgM antibodies are often insignificant.
- The major crossmatch tests compatibility between:
- Donor serum and recipient cells
- Donor cells and donor serum
- Recipient serum and donor red cells
- Recipient cells and recipient serum
Correct answer: Recipient serum and donor red cells
The major crossmatch combines recipient serum with donor red cells to detect antibodies in the recipient that could destroy transfused cells.
- Which antibody typically shows a characteristic 'dosage' effect, reacting more strongly with homozygous than heterozygous cells?
- Anti-Lewis a
- Anti-D
- Anti-K
- Anti-Jka
Correct answer: Anti-Jka
Kidd antibodies such as anti-Jka classically demonstrate dosage, reacting more strongly with cells from homozygous (Jka/Jka) individuals than heterozygotes.
- The most serious and immediate type of acute transfusion reaction, often fatal, is caused by:
- Iron overload
- ABO-incompatible transfusion causing intravascular hemolysis
- Febrile nonhemolytic reaction
- Allergic urticaria
Correct answer: ABO-incompatible transfusion causing intravascular hemolysis
ABO incompatibility triggers complement-mediated intravascular hemolysis with shock, DIC, and renal failure; it is usually due to clerical error and is the most dangerous acute reaction.
- Leukoreduction of cellular blood products primarily helps prevent:
- Iron overload
- ABO incompatibility
- Volume overload
- Febrile nonhemolytic reactions and CMV transmission
Correct answer: Febrile nonhemolytic reactions and CMV transmission
Removing white cells reduces febrile nonhemolytic transfusion reactions, HLA alloimmunization, and CMV transmission, since CMV resides in leukocytes.
- A 3+ reaction in the antibody screen at the antiglobulin phase with a negative autocontrol indicates:
- Autoantibody
- ABO discrepancy
- Rouleaux
- Alloantibody
Correct answer: Alloantibody
A positive screen with a negative autocontrol points to an alloantibody directed against foreign red cell antigens rather than the patient's own cells.
- Which is true regarding the weak D (Du) phenotype?
- These individuals are typed Rh positive as donors
- Weak D cannot be detected
- Weak D is the same as partial D
- These individuals are treated as Rh negative as donors
Correct answer: These individuals are typed Rh positive as donors
Weak D individuals express reduced D antigen and are labeled Rh positive as blood donors so recipients are not exposed to D antigen, even if initial typing is weak.
- Which Gram-positive cocci is catalase positive and coagulase positive?
- Enterococcus faecalis
- Staphylococcus epidermidis
- Staphylococcus aureus
- Streptococcus pyogenes
Correct answer: Staphylococcus aureus
Staphylococcus aureus is catalase positive (distinguishing staphylococci from streptococci) and coagulase positive (distinguishing it from coagulase-negative staphylococci).
- The oxidase test is used to presumptively identify which organism from a colony?
- Proteus mirabilis
- Klebsiella pneumoniae
- Escherichia coli
- Pseudomonas aeruginosa
Correct answer: Pseudomonas aeruginosa
Pseudomonas aeruginosa is oxidase positive, while members of Enterobacterales such as E. coli and Klebsiella are oxidase negative. The test detects cytochrome c oxidase.
- Beta-hemolysis on blood agar with bacitracin sensitivity is characteristic of:
- Streptococcus pneumoniae
- Enterococcus
- Streptococcus agalactiae
- Streptococcus pyogenes
Correct answer: Streptococcus pyogenes
Group A Streptococcus (S. pyogenes) shows beta-hemolysis and is susceptible to bacitracin (A disk), aiding presumptive identification.
- Which organism produces a green (alpha) hemolysis and is bile soluble and optochin sensitive?
- Staphylococcus saprophyticus
- Streptococcus viridans group
- Streptococcus pneumoniae
- Enterococcus faecalis
Correct answer: Streptococcus pneumoniae
Streptococcus pneumoniae is alpha-hemolytic, optochin susceptible, and bile soluble, distinguishing it from viridans streptococci which are optochin resistant and bile insoluble.
- On MacConkey agar, a strong lactose fermenter produces colonies that appear:
- Pink to red
- Black
- Colorless
- Green metallic
Correct answer: Pink to red
Lactose fermenters lower the pH and turn the neutral red indicator, producing pink to red colonies on MacConkey agar. Non-fermenters remain colorless.
- Which test differentiates Staphylococcus epidermidis from Staphylococcus saprophyticus?
- Oxidase
- Coagulase
- Catalase
- Novobiocin susceptibility
Correct answer: Novobiocin susceptibility
S. saprophyticus is novobiocin resistant whereas S. epidermidis is novobiocin susceptible. Both are coagulase-negative staphylococci.
- A curved, comma-shaped, oxidase-positive Gram-negative rod isolated from stool on TCBS agar producing yellow colonies suggests:
- Campylobacter jejuni
- Helicobacter pylori
- Vibrio cholerae
- Shigella
Correct answer: Vibrio cholerae
Vibrio cholerae is a curved oxidase-positive Gram-negative rod that ferments sucrose, producing yellow colonies on TCBS agar.
- The coagulase test detects an enzyme that converts:
- Glucose to lactate
- Fibrinogen to fibrin
- Plasminogen to plasmin
- Urea to ammonia
Correct answer: Fibrinogen to fibrin
Coagulase converts fibrinogen to fibrin, causing plasma to clot. A positive tube or slide coagulase identifies Staphylococcus aureus.
- Which organism is the most common cause of urinary tract infection and is a lactose-fermenting, indole-positive Gram-negative rod?
- Proteus mirabilis
- Klebsiella pneumoniae
- Escherichia coli
- Enterobacter cloacae
Correct answer: Escherichia coli
Escherichia coli is the leading cause of UTI; it ferments lactose and is indole positive, distinguishing it from many other Enterobacterales.
- The acid-fast (Ziehl-Neelsen) stain is used to identify which genus due to its mycolic acid cell wall?
- Neisseria
- Bacteroides
- Streptococcus
- Mycobacterium
Correct answer: Mycobacterium
Mycobacteria retain carbolfuchsin after acid-alcohol decolorization because of their waxy mycolic acid cell wall, appearing as red rods on acid-fast staining.
- Swarming motility on blood agar with a characteristic concentric pattern and urease positivity is typical of:
- Serratia marcescens
- Proteus mirabilis
- Klebsiella pneumoniae
- Pseudomonas aeruginosa
Correct answer: Proteus mirabilis
Proteus mirabilis swarms across the agar surface and is strongly urease positive, hydrolyzing urea rapidly. Its swarming can interfere with isolating other organisms.
- Which medium is selective for Neisseria gonorrhoeae?
- Modified Thayer-Martin agar
- MacConkey agar
- Hektoen enteric agar
- Mannitol salt agar
Correct answer: Modified Thayer-Martin agar
Modified Thayer-Martin agar contains antibiotics that inhibit normal flora, allowing recovery of fastidious Neisseria from genital and other specimens.
- A Gram-negative diplococcus from CSF that ferments maltose and glucose is:
- Neisseria meningitidis
- Moraxella catarrhalis
- Haemophilus influenzae
- Neisseria gonorrhoeae
Correct answer: Neisseria meningitidis
Neisseria meningitidis ferments both glucose and maltose, whereas N. gonorrhoeae ferments only glucose. Meningitidis is a cause of bacterial meningitis.
- The CAMP test is used to presumptively identify which beta-hemolytic streptococcus?
- Viridans group
- Group D (Enterococcus)
- Group B (S. agalactiae)
- Group A (S. pyogenes)
Correct answer: Group B (S. agalactiae)
Group B Streptococcus produces the CAMP factor, enhancing the beta-hemolysis of Staphylococcus aureus to form an arrowhead of hemolysis. It is hippurate positive too.
- Mannitol salt agar is selective and differential for:
- Staphylococci
- Streptococci
- Anaerobes
- Enterobacterales
Correct answer: Staphylococci
High salt selects for staphylococci; mannitol fermentation by S. aureus turns the phenol red indicator yellow, differentiating it from most coagulase-negative species.
- Which test rapidly identifies group A Streptococcus and Enterococcus by their resistance and growth in bile esculin or PYR?
- Catalase positive
- Oxidase positive
- Coagulase positive
- PYR positive in both group A Streptococcus and Enterococcus
Correct answer: PYR positive in both group A Streptococcus and Enterococcus
The PYR test (L-pyrrolidonyl-beta-naphthylamide hydrolysis) is positive for group A Streptococcus and Enterococcus, useful for presumptive identification.
- An obligate anaerobe that forms double-zone beta-hemolysis and is associated with gas gangrene is:
- Peptostreptococcus
- Bacteroides fragilis
- Clostridium perfringens
- Fusobacterium
Correct answer: Clostridium perfringens
Clostridium perfringens, a Gram-positive spore-forming anaerobic rod, produces a characteristic double zone of hemolysis and causes gas gangrene (myonecrosis).
- Which organism requires both X (hemin) and V (NAD) factors for growth?
- Legionella pneumophila
- Corynebacterium diphtheriae
- Haemophilus influenzae
- Bordetella pertussis
Correct answer: Haemophilus influenzae
Haemophilus influenzae requires both X and V factors, demonstrated by satellite growth around Staphylococcus on blood agar, which supplies V factor.
- The Kirby-Bauer disk diffusion method measures antimicrobial susceptibility by:
- Measuring zone of inhibition diameters
- Counting colonies
- Reading turbidity
- Detecting beta-lactamase color change
Correct answer: Measuring zone of inhibition diameters
In Kirby-Bauer, antibiotic diffuses from disks into a lawn of bacteria; the diameter of the inhibition zone is compared to standards to classify susceptible, intermediate, or resistant.
- The germ tube test is a rapid presumptive identification for which yeast?
- Cryptococcus neoformans
- Saccharomyces
- Candida albicans
- Candida glabrata
Correct answer: Candida albicans
Candida albicans produces germ tubes (true hyphal projections without constriction) when incubated in serum at 37 degrees C for a few hours, a rapid presumptive identification.
- A urease-positive curved Gram-negative rod associated with peptic ulcers and gastritis is:
- Salmonella
- Campylobacter jejuni
- Helicobacter pylori
- Vibrio parahaemolyticus
Correct answer: Helicobacter pylori
Helicobacter pylori is a strongly urease-positive curved Gram-negative rod that colonizes gastric mucosa and is a major cause of peptic ulcer disease.
- Which sugar reactions on TSI (triple sugar iron) agar indicate a non-lactose fermenter that produces H2S, such as Salmonella?
- Red slant/red butt
- Yellow slant/yellow butt with black
- Yellow slant/yellow butt, no gas
- Red slant/yellow butt with black precipitate
Correct answer: Red slant/yellow butt with black precipitate
An alkaline (red) slant with acid (yellow) butt indicates glucose-only fermentation; black precipitate from H2S production is characteristic of Salmonella on TSI.
- Which class of immunoglobulin is the first produced in a primary immune response?
Correct answer: IgM
IgM is the first antibody class produced during the primary immune response. Its pentameric structure makes it an efficient agglutinin and complement activator.
- The classical complement pathway is typically initiated by:
- Microbial surfaces alone
- Properdin
- Antigen-antibody (IgG or IgM) complexes binding C1q
- Mannose-binding lectin
Correct answer: Antigen-antibody (IgG or IgM) complexes binding C1q
The classical pathway begins when C1q binds the Fc region of antigen-bound IgM or IgG. The alternative and lectin pathways are antibody-independent.
- A positive rapid plasma reagin (RPR) test that is confirmed by a treponemal-specific test (FTA-ABS) indicates:
- Active or past syphilis infection
- Mononucleosis
- Lupus only
- Rheumatoid arthritis
Correct answer: Active or past syphilis infection
RPR is a nontreponemal screening test; reactivity confirmed by a treponemal test such as FTA-ABS supports a diagnosis of syphilis. Treponemal tests usually remain positive for life.
- Which antibody pattern indicates immunity to hepatitis B from vaccination?
- HBsAg positive, anti-HBs negative
- Anti-HBc IgM positive
- HBeAg positive
- Anti-HBs positive, anti-HBc negative
Correct answer: Anti-HBs positive, anti-HBc negative
Vaccination produces anti-HBs without anti-HBc, since the vaccine contains only surface antigen. Natural infection generates anti-HBc in addition to anti-HBs.
- The heterophile antibody (Monospot) test is used to support a diagnosis of:
- Rubella
- Cytomegalovirus
- Infectious mononucleosis (EBV)
- HIV
Correct answer: Infectious mononucleosis (EBV)
Infectious mononucleosis caused by Epstein-Barr virus generates heterophile antibodies that agglutinate horse or sheep red cells, the basis of the Monospot test.
- A fourfold or greater rise in antibody titer between acute and convalescent sera indicates:
- Cross-reactivity
- Recent or current infection
- Past immunity only
- Vaccine failure
Correct answer: Recent or current infection
A fourfold rise in titer in paired sera collected 2 to 3 weeks apart is the serologic standard for documenting recent or active infection.
- Which immunoglobulin is found in highest concentration in serum and is responsible for secondary immune responses?
Correct answer: IgG
IgG is the most abundant serum immunoglobulin and predominates in the secondary (memory) response. It is the only class that crosses the placenta.
- The prozone phenomenon causing a false-negative agglutination test is due to:
- Complement interference
- Antibody excess relative to antigen
- Antigen excess
- Antibody deficiency
Correct answer: Antibody excess relative to antigen
In the prozone, very high antibody concentration prevents lattice formation, giving a false-negative result. Diluting the serum restores proper antigen-antibody ratios.
- Anti-nuclear antibody (ANA) testing is most commonly used in the evaluation of:
- Allergic rhinitis
- Bacterial endocarditis
- Viral hepatitis
- Systemic lupus erythematosus
Correct answer: Systemic lupus erythematosus
ANA is a sensitive screening test for systemic lupus erythematosus and other autoimmune connective tissue diseases. Specific patterns and antibodies refine the diagnosis.
- The CD4 T-lymphocyte count is used primarily to monitor:
- Autoimmune disease
- HIV disease progression and immune status
- Hepatitis C
- Allergy severity
Correct answer: HIV disease progression and immune status
HIV preferentially infects and depletes CD4 T cells; the CD4 count is a key marker of immune competence and progression toward AIDS.
- Which test method uses an enzyme-labeled antibody with a substrate to produce a measurable color change?
- Western blot
- ELISA
- Immunofluorescence
- Latex agglutination
Correct answer: ELISA
The enzyme-linked immunosorbent assay (ELISA) uses an enzyme-conjugated antibody that converts substrate to a colored product, with intensity proportional to analyte concentration.
- Rheumatoid factor is an autoantibody most often of which class directed against the Fc portion of IgG?
Correct answer: IgM
Rheumatoid factor is classically an IgM antibody targeting the Fc region of IgG. It is associated with rheumatoid arthritis though not entirely specific.
- A positive anti-HBc IgM with HBsAg present indicates:
- Acute hepatitis B infection
- Resolved infection
- Immunity from vaccine
- Chronic carrier state
Correct answer: Acute hepatitis B infection
Anti-HBc IgM is the marker of acute hepatitis B; combined with HBsAg it reflects active acute infection rather than chronic disease or immunity.
- Which immunoglobulin mediates type I immediate hypersensitivity reactions?
Correct answer: IgE
IgE binds mast cells and basophils; cross-linking by allergen triggers degranulation and histamine release, mediating immediate hypersensitivity such as anaphylaxis and allergy.
- The confirmatory test traditionally used for a repeatedly reactive HIV screening immunoassay was:
- RPR
- Western blot or HIV-1/2 antibody differentiation assay
- Monospot
- C-reactive protein
Correct answer: Western blot or HIV-1/2 antibody differentiation assay
A repeatedly reactive HIV screen historically required Western blot confirmation; current algorithms use an HIV-1/HIV-2 antibody differentiation immunoassay and nucleic acid testing.
- Which urine color is most consistent with the presence of bilirubin?
- Red
- Cloudy white
- Pale yellow
- Dark amber/brown with yellow foam
Correct answer: Dark amber/brown with yellow foam
Conjugated bilirubin in urine produces a dark amber-brown color and a characteristic yellow foam when shaken, distinguishing it from concentrated normal urine.
- The presence of red blood cell casts in urine most specifically indicates:
- Contamination
- Lower urinary tract bleeding
- Dehydration
- Glomerular bleeding/glomerulonephritis
Correct answer: Glomerular bleeding/glomerulonephritis
RBC casts form in the renal tubules and indicate glomerular bleeding, characteristic of glomerulonephritis. Free RBCs without casts suggest lower tract or contamination.
- The reagent strip test for protein is most sensitive to which protein?
- Globulins
- Hemoglobin
- Albumin
- Bence Jones protein
Correct answer: Albumin
The protein error of indicators principle makes the reagent pad most sensitive to albumin. It may miss globulins and Bence Jones protein, which require other methods.
- A positive nitrite test on a urine dipstick suggests the presence of:
- Glucose
- Ketones
- Bilirubin
- Gram-negative bacteria that reduce nitrate to nitrite
Correct answer: Gram-negative bacteria that reduce nitrate to nitrite
Many Gram-negative bacteria such as E. coli reduce nitrate to nitrite, producing a positive nitrite test that supports a urinary tract infection. A negative result does not exclude infection.
- Which crystal, described as 'envelope' or octahedral shaped, is commonly found in normal acidic to neutral urine?
- Uric acid
- Calcium oxalate dihydrate
- Cystine
- Triple phosphate
Correct answer: Calcium oxalate dihydrate
Calcium oxalate dihydrate crystals have a classic envelope (octahedral) appearance and are common in normal urine. They may increase with ethylene glycol ingestion.
- The 'coffin lid' shaped crystal seen in alkaline urine is:
- Calcium oxalate
- Uric acid
- Triple phosphate (ammonium magnesium phosphate)
- Tyrosine
Correct answer: Triple phosphate (ammonium magnesium phosphate)
Triple phosphate (struvite) crystals appear as colorless prisms resembling coffin lids in alkaline urine and are associated with urease-producing organisms like Proteus.
- A urine specific gravity that remains fixed near 1.010 regardless of hydration indicates:
- Normal concentrating ability
- Diabetes insipidus only
- Glucosuria
- Isosthenuria from renal tubular dysfunction
Correct answer: Isosthenuria from renal tubular dysfunction
Isosthenuria, a fixed specific gravity matching plasma ultrafiltrate (about 1.010), reflects loss of the kidney's ability to concentrate or dilute urine.
- Which CSF finding is most consistent with bacterial meningitis?
- Increased glucose, decreased protein
- Lymphocyte predominance with normal glucose
- Normal glucose and protein
- Decreased glucose, increased protein, neutrophil predominance
Correct answer: Decreased glucose, increased protein, neutrophil predominance
Bacterial meningitis classically shows low CSF glucose, elevated protein, and a neutrophilic pleocytosis, whereas viral meningitis typically shows lymphocytes and normal glucose.
- Hexagonal crystals in urine are diagnostic of which inherited condition?
- Cystinuria
- Leucine metabolism disorder
- Tyrosinemia
- Gout
Correct answer: Cystinuria
Colorless hexagonal cystine crystals are pathognomonic of cystinuria, an inherited defect of renal tubular reabsorption of cystine. They form in acidic urine.
- A urine reagent strip glucose test uses which enzyme system?
- Hexokinase
- Glucose oxidase/peroxidase
- Glucose-6-phosphate dehydrogenase
- Lactate dehydrogenase
Correct answer: Glucose oxidase/peroxidase
The dipstick uses glucose oxidase to form hydrogen peroxide, which peroxidase uses to oxidize a chromogen, producing a color proportional to glucose. It is specific for glucose.
- Synovial fluid analysis showing negatively birefringent needle-shaped crystals under polarized light indicates:
- Gout (monosodium urate)
- Septic arthritis
- Rheumatoid arthritis
- Pseudogout (CPPD)
Correct answer: Gout (monosodium urate)
Monosodium urate crystals of gout are needle-shaped and negatively birefringent. CPPD crystals of pseudogout are rhomboid and positively birefringent.
- Waxy casts with a high refractive index and broad form most often indicate:
- Chronic renal failure and urinary stasis
- Acute infection
- Strenuous exercise
- Normal hydration
Correct answer: Chronic renal failure and urinary stasis
Waxy and broad casts form in dilated tubules with prolonged stasis, indicating chronic renal failure. They represent the final stage of cast degeneration.
- A high-protein pleural fluid with a fluid-to-serum protein ratio greater than 0.5 is classified as a:
- Normal fluid
- Exudate
- Transudate
- Chylous effusion
Correct answer: Exudate
By Light's criteria, an exudate has a pleural fluid-to-serum protein ratio greater than 0.5, suggesting inflammation, infection, or malignancy rather than a transudate from systemic causes.
- Ketones detected on a urine dipstick most strongly react with which ketone body?
- Beta-hydroxybutyrate
- Pyruvate
- Acetone only
- Acetoacetate
Correct answer: Acetoacetate
The nitroprusside reagent reacts strongly with acetoacetate and weakly with acetone, but does not detect beta-hydroxybutyrate, which is the predominant ketone in DKA.
- A positive leukocyte esterase test on urine dipstick indicates the presence of:
- Protein
- Red blood cells
- Glucose
- Neutrophils (white blood cells)
Correct answer: Neutrophils (white blood cells)
Leukocyte esterase is released from granulocytes; a positive result indicates neutrophils (pyuria) and supports urinary tract infection even after cells lyse.
- Which seminal fluid parameter is assessed first because viscosity and liquefaction affect other measurements?
- Morphology
- Liquefaction and appearance
- Sperm concentration
- Motility grading
Correct answer: Liquefaction and appearance
Semen normally liquefies within 30 to 60 minutes; assessing liquefaction and appearance first is necessary because abnormal viscosity interferes with accurate counting and motility.
- In which CSF tube collected during a lumbar puncture is the cell count and differential typically performed?
- Tube 3 (or last collected)
- Tube 1
- Any random tube
- Tube 2 for microbiology
Correct answer: Tube 3 (or last collected)
Tube 3 or the last tube is used for cell counts because it is least likely to be contaminated by a traumatic tap. Tube 1 is often reserved for chemistry, tube 2 for microbiology.
- Maltese cross formation under polarized light in urine indicates the presence of:
- Cholesterol or oval fat bodies (lipiduria)
- Uric acid crystals
- Red blood cells
- Bacteria
Correct answer: Cholesterol or oval fat bodies (lipiduria)
Lipids such as cholesterol esters in oval fat bodies produce a Maltese cross pattern under polarized light, seen in nephrotic syndrome with heavy proteinuria.
- Which of the following is the correct order of draw for a multitube venipuncture to prevent additive carryover?
- EDTA, sodium citrate, serum, heparin
- Blood culture, sodium citrate, serum, heparin, EDTA, fluoride
- Serum, EDTA, blood culture, heparin
- Fluoride, EDTA, heparin, citrate
Correct answer: Blood culture, sodium citrate, serum, heparin, EDTA, fluoride
The CLSI order of draw is blood culture, light blue (citrate), serum, green (heparin), lavender (EDTA), then gray (fluoride) to minimize cross-contamination of additives.
- A Levey-Jennings chart shows two consecutive control values both more than 2 SD on the same side of the mean. This violates which Westgard rule?
- 1-2s warning only
- 2-2s
- R-4s
- 1-3s
Correct answer: 2-2s
The 2-2s rule is violated when two consecutive controls exceed 2 SD on the same side of the mean, indicating systematic error and warranting run rejection.
- In the polymerase chain reaction, the step that separates double-stranded DNA into single strands is called:
- Ligation
- Annealing
- Extension
- Denaturation
Correct answer: Denaturation
Denaturation, typically at about 94 to 95 degrees C, breaks hydrogen bonds to separate the DNA strands. Annealing then allows primers to bind and extension synthesizes new strands.
- Which biosafety level is appropriate for routine clinical laboratory work with most bloodborne pathogens such as HIV and hepatitis B?
Correct answer: BSL-2
BSL-2 practices, including biosafety cabinets for aerosol-generating procedures and standard precautions, are appropriate for most clinical specimens and bloodborne pathogens.
- Accuracy of a laboratory method is best defined as:
- Closeness of a measured value to the true value
- The range of linearity
- Reproducibility of repeated measurements
- Smallest detectable amount
Correct answer: Closeness of a measured value to the true value
Accuracy refers to how close a result is to the true or accepted value, often assessed by recovery or reference materials. Precision describes reproducibility.
- A coefficient of variation (CV) is calculated as:
- Mean - SD
- SD×mean
- (SD/mean)×100
- (mean/SD)×100
Correct answer: (SD/mean)×100
The coefficient of variation expresses precision as a percentage: (standard deviation divided by mean) times 100. Lower CV indicates better reproducibility.
- The enzyme used in PCR that is heat-stable and synthesizes new DNA strands is:
- Reverse transcriptase
- DNA ligase
- Restriction endonuclease
- Taq polymerase
Correct answer: Taq polymerase
Taq polymerase, isolated from Thermus aquaticus, withstands the high denaturation temperatures of PCR, allowing automated thermal cycling without adding fresh enzyme.
- Which nucleic acid technique separates fragments by size using an electric field through a gel matrix?
- Sequencing
- Gel electrophoresis
- Southern blot hybridization
- PCR
Correct answer: Gel electrophoresis
Gel electrophoresis applies an electric field that moves negatively charged nucleic acids through a gel; smaller fragments migrate faster, separating fragments by size.
- Quality control material with values established to verify the analytical process should be run:
- Once per month
- Only during calibration
- Only when results look abnormal
- At defined intervals and with new reagent lots
Correct answer: At defined intervals and with new reagent lots
QC should be analyzed at regulatory-defined intervals, with new reagent lots, after maintenance, and per manufacturer instructions to ensure ongoing analytical validity.
- The federal regulation that governs the quality standards for all U.S. clinical laboratory testing on humans is:
Correct answer: CLIA
The Clinical Laboratory Improvement Amendments (CLIA) of 1988 establish quality standards for laboratory testing to ensure accuracy, reliability, and timeliness of results.
- Reverse transcriptase PCR (RT-PCR) is required when the starting template is:
- Double-stranded DNA
- Plasmid DNA
- Protein
- RNA
Correct answer: RNA
RT-PCR first uses reverse transcriptase to convert RNA into complementary DNA before amplification, allowing detection of RNA viruses and gene expression.
- A chemical that is both flammable and a health hazard should be stored according to information found on the:
- Procedure manual
- Calibration log
- Safety Data Sheet (SDS)
- Patient chart
Correct answer: Safety Data Sheet (SDS)
The Safety Data Sheet provides handling, storage, exposure, and emergency information for hazardous chemicals, required under the OSHA Hazard Communication Standard.
- A test with high sensitivity is best for:
- Screening to rule out disease (few false negatives)
- Confirming disease
- Measuring precision
- Detecting only severe cases
Correct answer: Screening to rule out disease (few false negatives)
High sensitivity means few false negatives, so a negative result reliably rules out disease, making such tests ideal for screening. Specificity is needed for confirmation.
- Real-time (quantitative) PCR differs from conventional PCR primarily because it:
- Cannot quantify the target
- Uses no primers
- Requires gel electrophoresis to read results
- Monitors amplification continuously using fluorescence
Correct answer: Monitors amplification continuously using fluorescence
Real-time PCR detects fluorescence proportional to product accumulation during each cycle, enabling quantification without post-amplification gel analysis.
- Which fire extinguisher class is appropriate for an electrical fire in the laboratory?
- Class K
- Class C
- Class D
- Class A
Correct answer: Class C
Class C extinguishers are designed for energized electrical equipment fires and use nonconductive agents. Class A is for ordinary combustibles and Class D for combustible metals.
- Delta checks in the laboratory compare:
- Two different patients
- Instrument to manual method
- Control to calibrator
- A patient's current result to a previous result for the same analyte
Correct answer: A patient's current result to a previous result for the same analyte
A delta check flags a significant difference between a patient's current and previous result for the same test, helping detect sample mislabeling or specimen errors.
- The standard precaution that assumes all patient specimens are potentially infectious is the basis of:
- Universal/standard precautions
- Reverse isolation
- Chemical hygiene
- Airborne isolation only
Correct answer: Universal/standard precautions
Standard (universal) precautions treat all blood and body fluids as potentially infectious, mandating barrier protection regardless of presumed patient status.
- Restriction endonucleases are enzymes that:
- Unwind RNA
- Cut DNA at specific recognition sequences
- Join DNA fragments
- Add poly-A tails
Correct answer: Cut DNA at specific recognition sequences
Restriction endonucleases recognize and cleave specific palindromic DNA sequences, producing reproducible fragments used in cloning and restriction fragment analysis.
- When a Levey-Jennings chart shows a steady drift of control values in one direction over several days, this trend most likely indicates:
- Random error
- Clerical error only
- Systematic error such as reagent deterioration
- Improved precision
Correct answer: Systematic error such as reagent deterioration
A gradual trend reflects systematic error, often from deteriorating reagents, aging calibration, or a failing light source, and requires investigation before reporting results.
- The buffy coat in a centrifuged anticoagulated blood specimen contains:
- Serum
- Plasma proteins
- White blood cells and platelets
- Red blood cells only
Correct answer: White blood cells and platelets
After centrifugation, the buffy coat is a thin gray-white layer between plasma and packed red cells containing leukocytes and platelets, sometimes used for cell harvesting.
- Which condition produces a positive osmotic fragility test due to decreased surface-to-volume ratio?
- Thalassemia
- Hereditary spherocytosis
- Iron deficiency anemia
- Sickle cell disease
Correct answer: Hereditary spherocytosis
Spherocytes have reduced surface area relative to volume, so they lyse in higher (less hypotonic) salt concentrations, producing increased osmotic fragility.
- Prolongation of the PT with a normal PTT most likely reflects a deficiency in which factor?
- Factor VIII
- Factor IX
- Factor VII
- Factor XII
Correct answer: Factor VII
Factor VII is unique to the extrinsic pathway measured by the PT. An isolated prolonged PT with normal PTT indicates factor VII deficiency or early warfarin effect.
- The activated partial thromboplastin time (aPTT) is used to monitor therapy with which anticoagulant?
- Unfractionated heparin
- Warfarin
- Aspirin
- Clopidogrel
Correct answer: Unfractionated heparin
The aPTT measures the intrinsic and common pathways and is used to monitor unfractionated heparin therapy. Warfarin is monitored with the PT/INR.
- Elevated D-dimer with prolonged PT and PTT, low fibrinogen, and thrombocytopenia is most consistent with:
- Hemophilia A
- Disseminated intravascular coagulation (DIC)
- Vitamin K deficiency
- Von Willebrand disease
Correct answer: Disseminated intravascular coagulation (DIC)
DIC consumes platelets and clotting factors while activating fibrinolysis, producing prolonged PT/PTT, low fibrinogen, thrombocytopenia, and elevated D-dimer.
- Which Clostridioides species causes antibiotic-associated pseudomembranous colitis and is detected by toxin or molecular testing of stool?
- Clostridioides difficile
- Clostridium tetani
- Clostridium botulinum
- Clostridium perfringens
Correct answer: Clostridioides difficile
Clostridioides difficile produces toxins A and B causing pseudomembranous colitis after antibiotic disruption of normal flora; testing detects the toxin gene or toxin.
- A Gram stain showing Gram-positive cocci in clusters from a wound, with a positive catalase and positive coagulase, identifies:
- Enterococcus
- Staphylococcus aureus
- Micrococcus
- Streptococcus pyogenes
Correct answer: Staphylococcus aureus
Gram-positive cocci in clusters that are catalase and coagulase positive are Staphylococcus aureus, a leading cause of wound and skin infections.
- After D, which Rh antigen is the most immunogenic and a frequent cause of alloimmunization?
- c (lowercase)
- C (uppercase)
- E
- e
Correct answer: c (lowercase)
After D, the c (lowercase) antigen is the most immunogenic in the Rh system; the approximate order of Rh immunogenicity is D > c > E > C > e. Anti-c is a common cause of hemolytic disease of the fetus and newborn. Note that c and C are distinct antigens — case matters.
- Group AB individuals are considered universal recipients of red cells because their plasma:
- Contains only anti-B
- Contains neither anti-A nor anti-B
- Contains only anti-A
- Contains both anti-A and anti-B
Correct answer: Contains neither anti-A nor anti-B
Group AB individuals lack anti-A and anti-B antibodies, allowing them to receive red cells of any ABO type, making them universal red cell recipients.
- Which marker is used to assess long-term average blood glucose and is reported as a percentage of total hemoglobin?
- Fasting glucose
- Hemoglobin A1c
- C-peptide
- Fructosamine
Correct answer: Hemoglobin A1c
Hemoglobin A1c, expressed as a percentage of glycated hemoglobin, reflects average glucose over 2 to 3 months and is used for diabetes diagnosis and monitoring.
- An increased osmolal gap (measured minus calculated osmolality) should raise suspicion for ingestion of:
- Glucose
- Ethanol or ethylene glycol
- Potassium
- Sodium chloride
Correct answer: Ethanol or ethylene glycol
Unmeasured osmotically active substances such as ethanol, methanol, or ethylene glycol raise measured osmolality above the calculated value, widening the osmolal gap.
- The reference (gold standard) anticoagulant for coagulation testing such as PT and PTT is:
- Lithium heparin
- Sodium citrate 3.2 percent
- EDTA
- Sodium fluoride
Correct answer: Sodium citrate 3.2 percent
Sodium citrate (light blue top) reversibly binds calcium and is required for coagulation studies; the 9:1 blood-to-anticoagulant ratio must be maintained for accuracy.
- Which finding distinguishes a partial D (mosaic) phenotype from weak D in terms of transfusion risk?
- They are indistinguishable clinically
- Weak D always forms anti-D
- Partial D individuals can make anti-D to the missing epitopes
- Partial D individuals never form antibodies
Correct answer: Partial D individuals can make anti-D to the missing epitopes
Partial D patients lack some D epitopes and can form alloanti-D against the missing portions if exposed, so as recipients they are often managed as Rh negative.
- A nucleic acid amplification test (NAAT) is preferred for diagnosing Chlamydia trachomatis because it offers:
- Ability to determine antibiotic susceptibility
- High sensitivity and specificity on noninvasive specimens
- Lower cost than culture only
- Detection of viable organisms only
Correct answer: High sensitivity and specificity on noninvasive specimens
NAATs are highly sensitive and specific for Chlamydia trachomatis and can be performed on urine and self-collected swabs, replacing the difficult and less sensitive culture.
- C-reactive protein is best characterized as:
- An acute phase reactant that rises rapidly with inflammation
- A clotting factor
- A tumor marker
- A liver enzyme
Correct answer: An acute phase reactant that rises rapidly with inflammation
CRP is an acute phase protein synthesized by the liver that rises quickly in response to inflammation or infection and falls rapidly when the stimulus resolves.
- Which body fluid finding indicates a chylous effusion?
- Low protein
- High pH
- High glucose
- Elevated triglycerides with milky appearance
Correct answer: Elevated triglycerides with milky appearance
Chylous effusions result from lymphatic (thoracic duct) leakage and contain high triglycerides, giving a milky appearance. Triglyceride levels above 110 mg/dL support the diagnosis.
- The most appropriate stain to identify Cryptococcus neoformans in cerebrospinal fluid is:
- Gram stain
- Acid-fast stain
- Wright stain
- India ink (or cryptococcal antigen testing)
Correct answer: India ink (or cryptococcal antigen testing)
India ink reveals the wide polysaccharide capsule of Cryptococcus neoformans as a clear halo in CSF, though cryptococcal antigen testing is more sensitive and now preferred.
- Which immunoglobulin predominates in secretions such as saliva, tears, and breast milk?
Correct answer: IgA
Secretory IgA is the main immunoglobulin in mucosal secretions, protecting mucosal surfaces. It exists as a dimer joined by a J chain and secretory component.
- A potassium result of 9.0 mEq/L on a hemolyzed specimen with no clinical correlation should be handled by:
- Diluting and reporting
- Recollecting the specimen and noting hemolysis
- Averaging with a prior value
- Reporting the result immediately
Correct answer: Recollecting the specimen and noting hemolysis
Hemolysis falsely elevates potassium; without clinical correlation the proper action is to note hemolysis and recollect, since reporting an artifactual critical value could harm the patient.
- Which feature differentiates serum from plasma?
- Serum contains anticoagulant
- Serum contains fibrinogen, plasma does not
- Plasma contains fibrinogen and clotting factors, serum does not
- They are identical
Correct answer: Plasma contains fibrinogen and clotting factors, serum does not
Plasma is the liquid from anticoagulated blood and retains fibrinogen and clotting factors; serum is obtained after clotting, so fibrinogen and consumed clotting factors are absent.
- A laboratory runs a control material 20 times and obtains a mean of 100 mg/dL with a standard deviation of 4 mg/dL. What is the coefficient of variation for this assay?
- 4 percent
- 0.04 percent
- 25 percent
- 40 percent
Correct answer: 4 percent
The coefficient of variation is 4 percent. CV equals the standard deviation divided by the mean, multiplied by 100, so (4/100)×100=4 percent. The CV expresses precision as a unitless relative percentage, which lets you compare variability between analytes that have very different concentrations.
- Two assays measure the same analyte. Method A has a mean of 50 mg/dL with an SD of 2 mg/dL; Method B has a mean of 200 mg/dL with an SD of 6 mg/dL. Which statement about their precision is correct?
- Method A is more precise because it has a lower CV of 4 percent versus 3 percent for B
- Method B is more precise because its SD is larger
- Method B is more precise because it has a lower CV of 3 percent versus 4 percent for A
- Precision cannot be compared because the means differ
Correct answer: Method B is more precise because it has a lower CV of 3 percent versus 4 percent for A
Method B is more precise, with a CV of 3 percent versus 4 percent for Method A. CV equals SD divided by mean times 100: Method A is (2/50)×100=4 percent and Method B is (6/200)×100=3 percent. Comparing raw SDs is misleading because they are tied to concentration; the CV normalizes for the mean and is the correct precision comparison.
- In spectrophotometry, Beer's law states that absorbance is directly proportional to which of the following?
- The concentration of the analyte and the light path length
- The wavelength of the incident light
- The transmittance of the sample
- The temperature of the cuvette
Correct answer: The concentration of the analyte and the light path length
Absorbance is directly proportional to the concentration of the analyte and the path length of the light through the solution. Beer's law is expressed as A = a b c, where a is the molar absorptivity, b is the path length, and c is concentration. Because absorbance rises linearly with concentration, a spectrophotometer can quantify an unknown by comparing its absorbance to a standard.
- A standard solution of 10 mg/dL gives an absorbance of 0.250. A patient sample read on the same spectrophotometer gives an absorbance of 0.400. Using Beer's law, what is the concentration of the patient sample?
- 6.25 mg/dL
- 16 mg/dL
- 40 mg/dL
- 10 mg/dL
Correct answer: 16 mg/dL
The patient concentration is 16 mg/dL. Because absorbance is directly proportional to concentration under Beer's law, concentration equals (sample absorbance / standard absorbance) × standard concentration =(0.400/0.250)×10=16 mg/dL. This proportional comparison to a known standard is the foundation of endpoint spectrophotometric assays.
- What is the primary purpose of the multirule quality control procedures known as Westgard rules?
- To calibrate instruments before each analytical run
- To detect both random and systematic error while minimizing false rejection of acceptable runs
- To confirm patient identity before specimen collection
- To establish reference intervals for new analytes
Correct answer: To detect both random and systematic error while minimizing false rejection of acceptable runs
Westgard rules are designed to detect both random and systematic error in an analytical run while keeping false rejections low. They apply a combination of statistical control rules to quality control results plotted on Levey-Jennings charts. Using multiple rules together improves error detection compared with a single rule and reduces the false alarms caused by using simple 2 SD limits alone.
- Under the Westgard 1-3s rule, an analytical run is rejected when:
- One control falls between 2 and 3 standard deviations from the mean
- A single control result exceeds the mean plus or minus 3 standard deviations
- Three consecutive controls fall on the same side of the mean
- Three controls within a run differ by more than 3 standard deviations
Correct answer: A single control result exceeds the mean plus or minus 3 standard deviations
The 1-3s rule rejects the run when a single control measurement falls outside the mean plus or minus 3 standard deviations. A result this far from the mean is statistically improbable in a stable system and is most often a signal of random error. The 1-3s rule is one of the most commonly used rejection rules in the Westgard multirule scheme.
- A laboratory observes that two consecutive control values both exceed the mean plus 2 standard deviations. Which Westgard rule is violated, and what type of error does it most likely indicate?
- 2-2s rule, indicating systematic error
- R-4s rule, indicating random error
- 1-3s rule, indicating random error
- 10x rule, indicating systematic error
Correct answer: 2-2s rule, indicating systematic error
This violates the 2-2s rule, which most likely indicates systematic error. The 2-2s rule is triggered when two consecutive control values exceed the same mean plus 2 SD limit (or both exceed mean minus 2 SD). Because the controls drift to the same side of the mean, the rule points to a systematic shift such as a deteriorating reagent or a calibration problem rather than random scatter.
- On a Levey-Jennings chart, which type of analytical error is best described by control points that scatter widely on both sides of the mean with increasing distance from it?
- Carryover error, shown as a single outlier
- Random error, shown as increased imprecision
- Systematic error, shown as a trend
- Systematic error, shown as a shift
Correct answer: Random error, shown as increased imprecision
Wide scatter of control points on both sides of the mean reflects random error, seen as increased imprecision. Random error is unpredictable and affects the spread of results, often flagged by the 1-3s or R-4s rules. By contrast, systematic error moves controls consistently to one side of the mean as a shift (abrupt) or trend (gradual).
- A technologist reviews a Levey-Jennings chart and notices that control values have gradually moved from near the mean to consistently above the mean plus 1 SD over the past eight days. This pattern is best described as a:
- Outlier, suggesting a one-time pipetting mistake
- Shift, suggesting random error
- Trend, suggesting systematic error such as a deteriorating reagent or aging lamp
- Normal random distribution requiring no action
Correct answer: Trend, suggesting systematic error such as a deteriorating reagent or aging lamp
A gradual, progressive movement of control values in one direction is a trend, which suggests systematic error. Trends commonly result from a slowly deteriorating reagent, a gradually failing light source, or progressive calibration drift. A shift, by contrast, is an abrupt change to a new level that stays there, while random error produces scatter rather than a directional pattern.
- What does a Levey-Jennings chart plot to monitor an analytical method over time?
- Instrument temperature against ambient humidity
- Daily control values against the established mean and standard deviation limits
- Reagent lot numbers against expiration dates
- Patient results against published reference intervals
Correct answer: Daily control values against the established mean and standard deviation limits
A Levey-Jennings chart plots daily quality control values against the established mean, with horizontal lines drawn at plus and minus 1, 2, and 3 standard deviations. Watching where each control point falls and how points relate over time lets the technologist detect shifts, trends, and outliers. This visual tracking is the basis for applying Westgard rules.
- Which statement correctly distinguishes calibration from calibration verification?
- Calibration verification is required only for waived tests
- Calibration verification establishes the original response curve, while calibration only confirms it
- They are identical procedures performed at different times
- Calibration establishes the relationship between signal and concentration, while calibration verification confirms that the existing calibration remains valid
Correct answer: Calibration establishes the relationship between signal and concentration, while calibration verification confirms that the existing calibration remains valid
Calibration establishes the relationship between an instrument's signal and analyte concentration, while calibration verification confirms that an existing calibration is still producing accurate results across the reportable range. Verification uses materials of known concentration to check that the method has not drifted; if verification fails, a full recalibration is performed. The two are related but distinct quality processes.
- A delta check flags a patient result. What does a delta check compare?
- The current patient result to that same patient's previous result for the same test
- Two different analytes within the same patient sample
- The patient result to the population reference interval
- The patient result to the daily quality control mean
Correct answer: The current patient result to that same patient's previous result for the same test
A delta check compares a patient's current test result to that same patient's previous result for the same analyte within a defined time interval, usually 24 to 48 hours. A difference larger than the delta check limit triggers an alert. This post-analytical check helps catch specimen mislabeling, sample mix-ups, or analytical errors before results are reported.
- A potassium result of 6.9 mmol/L is generated on an inpatient. According to standard laboratory practice, this is a critical value, which requires the laboratory to:
- Hold the result until the next scheduled report time
- Repeat the test silently and report only if it remains abnormal
- Immediately notify a responsible caregiver and document the read-back
- Report it routinely with all other electrolytes
Correct answer: Immediately notify a responsible caregiver and document the read-back
A critical value such as a potassium of 6.9 mmol/L must be communicated immediately to a responsible caregiver, and the laboratory must document the notification, including a read-back of the result for accuracy. Critical values represent results so far outside the normal range that they may be life threatening and demand prompt action. Routine batch reporting would dangerously delay intervention.
- Which set of results would most appropriately be defined as critical (panic) values requiring immediate notification?
- A normal calcium and a slightly low albumin
- A glucose of 28 mg/dL and a platelet count of 12,000 per microliter
- A hemoglobin of 13.5 g/dL and a sodium of 140 mmol/L
- A mildly elevated cholesterol and a borderline glucose
Correct answer: A glucose of 28 mg/dL and a platelet count of 12,000 per microliter
A glucose of 28 mg/dL and a platelet count of 12,000 per microliter are critical values that require immediate notification. Critical values are results so far outside the reference range that they signal an immediately life-threatening situation, such as severe hypoglycemia or severe thrombocytopenia with bleeding risk. Mildly abnormal or normal results do not meet the threshold for urgent caregiver notification.
- According to the CLSI recommended order of draw, which tube is collected immediately after a blood culture bottle?
- Light blue (sodium citrate) coagulation tube
- Gray (sodium fluoride) tube
- Green (heparin) tube
- Lavender (EDTA) tube
Correct answer: Light blue (sodium citrate) coagulation tube
The light blue sodium citrate coagulation tube is drawn immediately after blood culture collection. The CLSI order of draw is blood culture, then light blue, then serum or SST, then green, then lavender, then gray. Drawing the coagulation tube early minimizes contamination from other tube additives that could interfere with clotting tests such as PT and aPTT.
- Why must an EDTA (lavender) tube be drawn after the light blue sodium citrate tube in the order of draw?
- EDTA carryover can chelate calcium and falsely prolong coagulation results in the citrate tube
- The order has no analytical basis and is purely traditional
- EDTA tubes must always be filled first to prevent hemolysis
- Sodium citrate carryover would clot the EDTA tube
Correct answer: EDTA carryover can chelate calcium and falsely prolong coagulation results in the citrate tube
EDTA is drawn after the citrate tube because EDTA carryover chelates calcium, and contaminating a coagulation specimen would falsely prolong clotting times such as PT and aPTT. The order of draw is designed to prevent additive cross-contamination from one tube affecting the next. Potassium-EDTA carryover can also falsely elevate potassium and lower calcium in downstream tubes.
- What additive is present in a lavender (purple) top blood collection tube, and what is its mechanism of action?
- EDTA, which chelates calcium to prevent clotting
- Lithium heparin, which inhibits thrombin
- Sodium fluoride, which inhibits glycolysis
- Sodium citrate, which binds calcium reversibly
Correct answer: EDTA, which chelates calcium to prevent clotting
The lavender top tube contains EDTA, which prevents clotting by chelating (binding) calcium ions that are required for the coagulation cascade. EDTA is the anticoagulant of choice for hematology testing such as the CBC because it preserves cell morphology and prevents platelet clumping. Sodium fluoride, sodium citrate, and heparin are additives found in other tube types.
- A coagulation specimen is collected in a light blue sodium citrate tube. What is the correct ratio of blood to anticoagulant required for accurate results?
- 1 part blood to 4 parts citrate
- 9 parts blood to 1 part citrate
- 4 parts blood to 1 part citrate
- 1 part blood to 9 parts citrate
Correct answer: 9 parts blood to 1 part citrate
The correct ratio is 9 parts blood to 1 part sodium citrate (a 9:1 ratio), which is why the tube must be filled completely. Underfilling raises the relative citrate concentration, binds excess calcium, and falsely prolongs clotting times such as PT and aPTT. Maintaining the proper fill volume preserves the anticoagulant-to-plasma balance the test was standardized against.
- A specimen for forensic drug testing must maintain a documented chain of custody. The primary purpose of chain-of-custody documentation is to:
- Provide a continuous written record of specimen possession and handling for legal defensibility
- Confirm the specimen was collected in the correct anticoagulant tube
- Verify that the analyzer was calibrated on the day of testing
- Ensure the specimen was tested within its stability window
Correct answer: Provide a continuous written record of specimen possession and handling for legal defensibility
Chain-of-custody documentation provides a continuous, written record of who possessed and handled the specimen from collection through testing and storage, ensuring the result is legally defensible. Every transfer is dated, timed, and signed so the sample's integrity and identity cannot be questioned in court. This rigorous tracking is required for forensic and employment drug testing.
- A control result falls 2.5 standard deviations above the mean. Under a Westgard scheme that uses the 1-2s rule only as a warning, the appropriate next step is to:
- Immediately reject the run and report no patient results
- Treat 1-2s as a warning and apply additional rejection rules before deciding
- Discard the control and report patient results without review
- Recalibrate the instrument before any further action
Correct answer: Treat 1-2s as a warning and apply additional rejection rules before deciding
A single control between 2 and 3 SD violates the 1-2s warning rule, which should trigger inspection using additional rejection rules rather than automatic rejection. The 1-2s rule alone has a high false-rejection rate, so it is used as a warning that prompts evaluation of rules such as 2-2s, R-4s, 4-1s, or 10x. Only when a true rejection rule is violated is the run rejected.
- A technologist needs to prepare 100 mL of a 1:5 dilution of a serum sample in saline. How much serum and how much diluent are required?
- 25 mL serum and 75 mL saline
- 20 mL serum and 80 mL saline
- 5 mL serum and 95 mL saline
- 50 mL serum and 50 mL saline
Correct answer: 20 mL serum and 80 mL saline
A 1:5 dilution means 1 part sample in a total of 5 parts, so 100 mL total requires 20 mL serum and 80 mL saline. The dilution ratio expresses the volume of sample relative to the total final volume, not sample to diluent. Diluting and then multiplying the measured result by the dilution factor of 5 lets the laboratory bring an overly concentrated analyte into the linear range.
- A serum sample reads above the analytical measurement range, so the technologist performs a 1:10 dilution and re-runs it, obtaining 45 mg/dL on the diluted sample. What result should be reported for the original specimen?
- 45 mg/dL
- 10 mg/dL
- 4.5 mg/dL
- 450 mg/dL
Correct answer: 450 mg/dL
The reported result is 450 mg/dL. When a sample is diluted to bring it into the measurable range, the result obtained on the diluted material must be multiplied by the dilution factor: 45 mg/dL×10=450 mg/dL. Forgetting to multiply by the dilution factor would report a falsely low value and is a common preanalytical-to-analytical calculation error.
- A control value abruptly jumps from running near the mean to consistently sitting about 2 SD above the mean and stays there. On a Levey-Jennings chart this pattern is classified as a:
- Trend, indicating a gradually failing reagent
- Increase in imprecision, indicating random error
- Shift, indicating an abrupt systematic change such as a new reagent lot or recalibration
- Outlier, indicating a single random error
Correct answer: Shift, indicating an abrupt systematic change such as a new reagent lot or recalibration
An abrupt change to a new level that then remains stable is a shift, indicating systematic error. Shifts commonly follow a discrete event such as a new reagent lot, a fresh calibration, or a change in instrument component. This differs from a trend, which moves gradually, and from random error, which produces scatter rather than a sustained offset.
- A diabetic patient's random urine returns an albumin-to-creatinine ratio (ACR) of 120 mg/g. Using the standard KDIGO albuminuria categories, how should this result be classified?
- Severely increased (A3)
- Nephrotic-range proteinuria
- Moderately increased (A2)
- Normal to mildly increased (A1)
Correct answer: Moderately increased (A2)
An ACR of 120 mg/g falls in the moderately increased albuminuria category (A2), defined as 30 to 300 mg/g. This range, historically called 'microalbuminuria,' is below the normal-to-mild cutoff of under 30 mg/g (A1) and below the severely increased threshold of over 300 mg/g (A3). Urine microalbumin testing detects albumin too low for a routine dipstick and is used to screen diabetics for early diabetic nephropathy.
- Why is a urine albumin-to-creatinine ratio (ACR) on a random specimen preferred over a simple urine albumin concentration for microalbumin screening?
- Albumin is unstable unless measured against creatinine
- The ACR removes the need for any reference range
- Creatinine correction compensates for urine dilution and concentration variability
- Creatinine inhibits bacterial degradation of albumin
Correct answer: Creatinine correction compensates for urine dilution and concentration variability
Correcting albumin to urine creatinine compensates for variable urine dilution and concentration in a random (spot) specimen, so a single untimed sample approximates a 24-hour albumin estimate. A bare albumin concentration would swing with how dilute or concentrated the urine is. The ratio does not replace reference ranges (KDIGO categories still apply) and creatinine has no antibacterial role here.
- A glucose result is reported as 162 mg/dL. Converted to SI units, what is the approximate value in mmol/L?
- 9.0 mmol/L
- 18.0 mmol/L
- 29.2 mmol/L
- 1.62 mmol/L
Correct answer: 9.0 mmol/L
162 mg/dL equals about 9.0 mmol/L. To convert glucose from mg/dL to mmol/L, multiply by 0.0555 (the reciprocal of glucose's molar mass relationship): 162 x 0.0555 = 9.0. Equivalently, dividing the mg/dL value by 18 gives the same result. Multiplying by 18 instead of dividing would have produced the erroneous 29.2 figure.
- A laboratory must report creatinine in SI units (µmol/L). A serum creatinine of 1.2 mg/dL converts to approximately which value?
- 13.6 µmol/L
- 106 µmol/L
- 240 µmol/L
- 68 µmol/L
Correct answer: 106 µmol/L
1.2 mg/dL of creatinine equals about 106 µmol/L. The conversion factor for creatinine from mg/dL to µmol/L is 88.4: 1.2 x 88.4 = 106. Each analyte has its own factor based on molecular weight, so the glucose factor of 0.0555 or 18 must not be applied to creatinine.
- Creatinine clearance is used as an estimate of which physiologic measurement?
- Effective osmolar clearance
- Glomerular filtration rate (GFR)
- Tubular secretion capacity
- Renal blood flow
Correct answer: Glomerular filtration rate (GFR)
Creatinine clearance estimates the glomerular filtration rate (GFR). Because creatinine is filtered at the glomerulus and only minimally secreted by the tubules, the volume of plasma cleared of creatinine per unit time approximates GFR. It slightly overestimates true GFR due to that small tubular secretion, but it remains a practical clearance measure. It does not measure total renal blood flow or osmolar clearance.
- A 24-hour urine collection yields a urine creatinine of 90 mg/dL, urine volume of 1,440 mL/day, and serum creatinine of 1.0 mg/dL. Using the standard formula, what is the creatinine clearance?
- 144 mL/min
- 129 mL/min
- 63 mL/min
- 90 mL/min
Correct answer: 90 mL/min
The creatinine clearance is about 90 mL/min. The formula is (U×V)/P, where U is urine creatinine (90 mg/dL), V is urine flow in mL/min, and P is serum creatinine (1.0 mg/dL). 1,440 mL/day divided by 1,440 min/day equals 1.0 mL/min, so (90×1.0)/1.0=90 mL/min. Forgetting to convert daily volume to mL/min is the most common error.
- A technologist must prepare a 1:20 dilution of serum to bring a high analyte into the measuring range. Which volumes correctly produce this dilution in a final volume of 2.0 mL?
- 0.1 mL serum plus 2.0 mL diluent
- 1.0 mL serum plus 1.0 mL diluent
- 0.1 mL serum plus 1.9 mL diluent
- 0.2 mL serum plus 1.8 mL diluent
Correct answer: 0.1 mL serum plus 1.9 mL diluent
0.1 mL of serum plus 1.9 mL of diluent gives a 1:20 dilution. A 1:20 dilution means 1 part sample in 20 total parts, so the sample is one-twentieth of the final volume: 2.0 mL/20=0.1 mL serum, with the remaining 1.9 mL as diluent. The result must then be multiplied by 20 to recover the original concentration.
- A diluted specimen read as 45 mg/dL after a 1:5 dilution. What is the reported concentration of the original undiluted sample?
- 225 mg/dL
- 45 mg/dL
- 250 mg/dL
- 9 mg/dL
Correct answer: 225 mg/dL
The original concentration is 225 mg/dL. The measured result on a diluted sample must be multiplied by the dilution factor to recover the original value: 45×5=225 mg/dL. Dividing by the dilution factor (yielding 9) is the classic mistake, since dilution lowers the measured value and the math must reverse that.
- In the hexokinase reference method for serum glucose, the absorbance change actually measured by the spectrophotometer is produced by which reaction step?
- Oxidation of glucose to gluconic acid by glucose oxidase
- Phosphorylation of glucose to glucose-6-phosphate
- Reduction of NADP+ to NADPH by glucose-6-phosphate dehydrogenase
- Cleavage of a chromogenic peroxide complex
Correct answer: Reduction of NADP+ to NADPH by glucose-6-phosphate dehydrogenase
The measured signal comes from the reduction of NADP+ to NADPH catalyzed by glucose-6-phosphate dehydrogenase, which is monitored as increasing absorbance at 340 nm. Hexokinase first phosphorylates glucose, but that step produces no chromophore. Glucose oxidase and peroxide-chromogen chemistry belong to the alternative glucose oxidase method, not the hexokinase method.
- A serum potassium is reported as 6.8 mmol/L on a hemolyzed specimen from an otherwise healthy outpatient with a normal ECG. What is the most appropriate technologist action?
- Note the hemolysis and request a fresh, properly collected specimen
- Subtract a fixed correction factor and report the adjusted value
- Dilute the sample and rerun to lower the value
- Report the result without comment
Correct answer: Note the hemolysis and request a fresh, properly collected specimen
The correct action is to note the hemolysis and request a fresh, properly collected specimen. Potassium is far more concentrated inside red cells than in plasma, so hemolysis releases intracellular potassium and falsely elevates the serum value (pseudohyperkalemia). No validated fixed correction factor exists, and diluting does not fix the pre-analytical contamination; a new clean draw is required.
- A blood gas reports pH 7.32, pCOX2 30 mmHg, and HCOX3 15 mmol/L. Which acid-base disturbance does this pattern represent?
- Metabolic acidosis with respiratory compensation
- Respiratory alkalosis
- Respiratory acidosis
- Metabolic alkalosis
Correct answer: Metabolic acidosis with respiratory compensation
This pattern represents metabolic acidosis with respiratory compensation. The low pH indicates acidemia, and the low bicarbonate (15 mmol/L, below the roughly 22 to 26 reference range) identifies the primary metabolic process. The low pCOX2 shows the lungs are blowing off COX2 to partially compensate. In a primary respiratory acidosis, pCOX2 would be elevated rather than low.
- A patient has a measured serum osmolality of 320 mOsm/kg but a calculated osmolality of 295 mOsm/kg. This osmolal gap of 25 most strongly suggests which clinical situation?
- Ingestion of a low-molecular-weight toxin such as methanol or ethylene glycol
- Hyperkalemia
- Iron-deficiency anemia
- Chronic kidney disease
Correct answer: Ingestion of a low-molecular-weight toxin such as methanol or ethylene glycol
An elevated osmolal gap points to ingestion of a low-molecular-weight, osmotically active toxin such as methanol or ethylene glycol. The calculated osmolality includes only sodium, glucose, and urea, so an unmeasured osmole widens the gap between measured and calculated values. A gap above about 10 to 15 is abnormal. Chronic kidney disease and electrolyte changes are captured by the calculated value and do not by themselves widen the gap.
- To screen for early glomerular damage in a diabetic patient whose routine urine dipstick protein is negative, which test is most appropriate?
- Serum total protein
- Urine microalbumin (albumin-to-creatinine ratio)
- Urine specific gravity
- Serum protein electrophoresis
Correct answer: Urine microalbumin (albumin-to-creatinine ratio)
Urine microalbumin testing, reported as the albumin-to-creatinine ratio, is the appropriate screen for early glomerular damage. A standard dipstick only detects albumin above roughly 300 mg/L, so it misses the moderately increased range (30 to 300 mg/g ACR) that signals early diabetic nephropathy. Serum total protein and electrophoresis assess different problems, and specific gravity measures concentration, not protein loss.
- A total cholesterol value of 232 mg/dL must be reported in SI units (mmol/L). Using the cholesterol conversion factor, the result is approximately:
- 42 mmol/L
- 4.2 mmol/L
- 6.0 mmol/L
- 12.9 mmol/L
Correct answer: 6.0 mmol/L
232 mg/dL of cholesterol equals about 6.0 mmol/L. Cholesterol is converted by dividing the mg/dL value by 38.67 (or multiplying by 0.0259): 232 / 38.67 = 6.0. Because each analyte's factor depends on its molecular weight, the glucose factor of 0.0555 cannot be substituted here, which would have wrongly produced about 12.9.
- Using the Friedewald equation with total cholesterol 200 mg/dL, HDL 50 mg/dL, and triglycerides 150 mg/dL, what is the calculated LDL cholesterol?
- 130 mg/dL
- 100 mg/dL
- 150 mg/dL
- 120 mg/dL
Correct answer: 120 mg/dL
The calculated LDL is 120 mg/dL. The Friedewald equation is LDL = total cholesterol minus HDL minus (triglycerides / 5), so 200−50−(150/5)=200−50−30=120 mg/dL. The triglyceride term estimates VLDL cholesterol. This equation is invalid when triglycerides exceed about 400 mg/dL, where the VLDL estimate breaks down.
- A patient has a total serum calcium of 7.6 mg/dL with a serum albumin of 2.0 g/dL. After correcting for the low albumin, the calcium is most likely:
- Still markedly low (true hypocalcemia)
- Near the normal range (corrected for hypoalbuminemia)
- Critically high
- Unmeasurable without ionized calcium
Correct answer: Near the normal range (corrected for hypoalbuminemia)
After correction, the calcium is near normal. Roughly half of serum calcium is bound to albumin, so a low albumin lowers total calcium without changing the physiologically active ionized fraction. The common correction adds 0.8 mg/dL of calcium for every 1.0 g/dL the albumin sits below 4.0 g/dL: 4.0−2.0=2.0, so 2.0×0.8=1.6, giving a corrected calcium of about 9.2 mg/dL, within the normal range.
- In an ion-selective electrode (ISE) measurement of serum sodium, the electrode generates a signal that is proportional to which property?
- The osmolality of the specimen
- The activity (effective concentration) of sodium ions
- The light absorbed by sodium complexes
- The total mass of sodium in the sample
Correct answer: The activity (effective concentration) of sodium ions
An ion-selective electrode responds to the activity of the target ion, generating a voltage proportional to sodium ion activity per the Nernst relationship. Direct ISE methods therefore are not affected by the volume occupied by lipids or proteins, unlike flame photometry or indirect methods that can show pseudohyponatremia. ISE does not measure mass, osmolality, or light absorbance.
- A markedly lipemic serum specimen is submitted for multiple chemistry tests. Which analyte result is most likely to be falsely altered by this turbidity on a spectrophotometric method?
- Sodium measured by direct ISE
- Chloride measured by coulometry
- Potassium measured by direct ISE
- Total bilirubin measured spectrophotometrically
Correct answer: Total bilirubin measured spectrophotometrically
Spectrophotometric total bilirubin is most susceptible because lipemic turbidity scatters and absorbs light, falsely shifting the optical reading. Direct ISE methods for sodium and potassium and coulometric chloride do not rely on light transmission, so they are largely unaffected by turbidity. Recognizing which methods are optical versus electrochemical predicts which results lipemia will distort.
- A patient with severe anemia has a reticulocyte count of 8 percent and a hematocrit of 22 percent. Using a normal hematocrit of 45 percent, what is the corrected reticulocyte count?
- 1.8 percent
- 3.9 percent
- 16.4 percent
- 8.0 percent
Correct answer: 3.9 percent
The corrected reticulocyte count is 3.9 percent. The correction adjusts the raw percentage for the degree of anemia using the formula reticulocyte percent multiplied by (patient hematocrit divided by 45). Here 8×22/45 equals about 3.9 percent. Reporting the raw 8 percent would falsely overstate marrow output, because a low hematocrit inflates the percentage of reticulocytes relative to the shrunken red cell mass.
- A CBC reports a total white blood cell count of 12.0×109/L with a differential of 60 percent segmented neutrophils and 8 percent bands. What is the absolute neutrophil count?
- 6.0×109/L
- 8.16×109/L
- 7.2×109/L
- 0.68×109/L
Correct answer: 8.16×109/L
The absolute neutrophil count is 8.16×109/L. The ANC is calculated as the total WBC count multiplied by the combined fraction of segmented neutrophils plus bands: 12.0 multiplied by (0.60 + 0.08) equals 8.16. Bands must be included because they are mature-functioning neutrophils; omitting them (using only segs) would underestimate the count at 7.2.
- A peripheral smear differential reports an increased number of band neutrophils and occasional metamyelocytes. On a CBC report, this finding is described as a:
- Right shift
- Leukoerythroblastic reaction
- Relative lymphocytosis
- Left shift
Correct answer: Left shift
A left shift describes the release of immature neutrophilic cells such as bands and metamyelocytes into the circulating blood. It reflects accelerated granulopoiesis, classically with infection or inflammation. A right shift refers to hypersegmented neutrophils, and a leukoerythroblastic reaction additionally includes nucleated red cells and immature granulocytes together.
- Coarse basophilic stippling on a Wright-stained smear, representing aggregated ribosomal RNA, is most characteristically associated with which condition?
- Splenectomy
- Acute blood loss
- Lead poisoning
- Warm autoimmune hemolytic anemia
Correct answer: Lead poisoning
Lead poisoning is most characteristically associated with coarse basophilic stippling. Lead inhibits pyrimidine 5-prime nucleotidase, preventing degradation of ribosomal RNA, which aggregates into the punctate basophilic granules seen across the cell. Coarse stippling is also seen in thalassemia and sideroblastic anemia, but lead toxicity is the classic teaching example.
- A patient has a hemoglobin of 9.0 g/dL, a hematocrit of 27 percent, and a red blood cell count of 3.0×1012/L. What is the mean corpuscular hemoglobin concentration (MCHC)?
- 90.0 fL
- 30.0 g/dL
- 27.0 pg
- 33.3 g/dL
Correct answer: 33.3 g/dL
The MCHC is 33.3 g/dL. MCHC is calculated as hemoglobin divided by hematocrit, multiplied by 100: (9.0/27)×100 equals 33.3 g/dL, which falls in the normal range of about 32 to 36 g/dL. MCHC reports a concentration in g/dL, distinguishing it from MCV (a volume in fL) and MCH (content in pg).
- A leukemia panel shows blasts that are myeloperoxidase positive and contain Auer rods. Which leukemia does this distinguish from acute lymphoblastic leukemia?
- Chronic lymphocytic leukemia
- Hairy cell leukemia
- Burkitt lymphoma
- Acute myeloid leukemia
Correct answer: Acute myeloid leukemia
Acute myeloid leukemia is distinguished by myeloperoxidase-positive blasts and Auer rods, both markers of myeloid lineage. Acute lymphoblastic leukemia arises from lymphoid blasts that are myeloperoxidase negative, lack Auer rods, and are instead TdT positive. The presence of Auer rods essentially excludes a lymphoblastic process.
- A peripheral smear shows several red cells with one or two small, round, dense nuclear fragments. These Howell-Jolly bodies are removed in a healthy person by which organ?
- Kidney
- Liver
- Bone marrow
- Spleen
Correct answer: Spleen
The spleen normally removes Howell-Jolly bodies, which are residual fragments of nuclear DNA left in red cells. The splenic macrophages pit these inclusions during passage through the red pulp. When the spleen is absent or hypofunctional, the inclusions persist and become visible on the smear.
- A 70-year-old presents with marked fatigue, a hemoglobin of 7.5 g/dL, and an MCV of 118 fL. The smear shows oval macrocytes and hypersegmented neutrophils. Which deficiency most likely explains these findings?
- Vitamin B12 or folate deficiency
- Iron deficiency
- Copper excess
- Vitamin C deficiency
Correct answer: Vitamin B12 or folate deficiency
Vitamin B12 or folate deficiency most likely explains megaloblastic macrocytic anemia. These vitamins are required for DNA synthesis, so deficiency causes asynchronous nuclear and cytoplasmic maturation, producing large oval macrocytes and neutrophils with six or more lobes. Iron deficiency instead causes a microcytic, hypochromic picture with a low MCV.
- An adult is found to have a microcytic, hypochromic anemia with a normal-to-elevated ferritin, normal iron studies, and a markedly elevated red cell count for the degree of anemia. Which cause of microcytic anemia is most consistent?
- Iron deficiency
- Acute hemorrhage
- Folate deficiency
- Thalassemia trait
Correct answer: Thalassemia trait
Thalassemia trait is most consistent with these findings. It causes microcytosis from reduced globin chain synthesis rather than iron lack, so iron studies and ferritin are normal, and the RBC count is often disproportionately high relative to the anemia. Iron deficiency, by contrast, lowers ferritin and the RBC count and raises total iron-binding capacity.
- An emergency-department CBC reports a WBC of 88×109/L, hemoglobin 7.0 g/dL, platelets 18×109/L, and the differential shows 65 percent blasts. What is the most likely diagnosis category?
- Iron deficiency anemia
- Reactive leukocytosis from infection
- Polycythemia vera
- Acute leukemia
Correct answer: Acute leukemia
Acute leukemia is the most likely diagnosis when a markedly elevated WBC count is accompanied by a high percentage of circulating blasts plus anemia and thrombocytopenia. Blasts exceeding 20 percent in blood or marrow define acute leukemia. A reactive leukocytosis shows a left shift of maturing granulocytes, not a predominance of blasts, and usually preserves the red cell and platelet counts.
- During a manual reticulocyte count using new methylene blue, the technologist must count reticulocytes per 1000 red cells and may use a Miller disc to improve precision. The reticulocyte percentage is then converted to an absolute count by multiplying by which value?
- The red blood cell count
- The white blood cell count
- The hematocrit
- The platelet count
Correct answer: The red blood cell count
The reticulocyte percentage is multiplied by the red blood cell count to obtain the absolute reticulocyte count in cells per liter. The absolute count is preferred over the percentage because it is not skewed by changes in the total red cell mass. A Miller disc reduces counting error by restricting the area in which reticulocytes are tallied.
- A red cell histogram from an automated analyzer shows a single broad population with a high RDW, while the smear shows a dual population of both microcytic and normocytic cells. This dimorphic picture most suggests:
- Cold agglutinin disease
- Hereditary spherocytosis
- Acute promyelocytic leukemia
- A patient recently treated for iron deficiency or after transfusion
Correct answer: A patient recently treated for iron deficiency or after transfusion
A dimorphic population with a high RDW most suggests a patient recently treated for iron deficiency, in whom new normocytic cells coexist with older microcytic cells, or a recently transfused patient. The RDW quantifies anisocytosis and rises when two distinct size populations are present. Hereditary spherocytosis instead shows a high MCHC with uniform spherocytes.
- An emergency department patient presents with a markedly elevated D-dimer. Which of the following clinical situations is LEAST likely on its own to explain an isolated D-dimer elevation?
- Recent major surgery or trauma
- An inherited factor VII deficiency with no active clotting
- Acute venous thromboembolism such as a pulmonary embolus
- Advanced pregnancy or sepsis with systemic inflammation
Correct answer: An inherited factor VII deficiency with no active clotting
An inherited factor VII deficiency with no active clotting is the situation least likely to raise D-dimer, because D-dimer is a fibrin degradation product that rises only when cross-linked fibrin has been formed and then broken down by plasmin. Venous thromboembolism, surgery, trauma, pregnancy, malignancy, sepsis, and inflammation all generate and lyse fibrin, so they characteristically elevate D-dimer. A factor deficiency that prevents clot formation does not increase fibrin turnover and therefore does not, by itself, raise D-dimer.
- A patient has a prolonged aPTT that does not correct on a 1:1 mix with normal pooled plasma. The dilute Russell viper venom time (dRVVT) is prolonged on screen but shortens (corrects) when excess phospholipid is added in the confirmatory step. These results are most consistent with which finding?
- Vitamin K deficiency
- A lupus anticoagulant
- Hemophilia A (factor VIII deficiency)
- Disseminated intravascular coagulation
Correct answer: A lupus anticoagulant
A lupus anticoagulant is indicated by a phospholipid-dependent prolongation that fails to correct with normal plasma but corrects when excess phospholipid is added in the confirmatory phase. A lupus anticoagulant is an antibody directed against phospholipid, so it inhibits phospholipid-dependent clotting tests and is not overcome by supplying the missing factors in normal plasma. Adding excess phospholipid neutralizes the antibody and shortens the clotting time, confirming the phospholipid dependence. A simple factor deficiency such as hemophilia A would instead correct on the mixing study because normal plasma replaces the missing factor.
- A clinician asks the laboratory what the international normalized ratio (INR) actually measures and standardizes. Which statement is correct?
- It measures platelet aggregation in response to ristocetin
- It directly measures plasma heparin concentration in units per milliliter
- It quantifies the activity of the intrinsic pathway independent of the extrinsic pathway
- It standardizes the prothrombin time across different thromboplastin reagents to monitor warfarin therapy
Correct answer: It standardizes the prothrombin time across different thromboplastin reagents to monitor warfarin therapy
The INR standardizes the prothrombin time (PT) across different thromboplastin reagents so that results are comparable between laboratories and can be used to monitor warfarin (vitamin K antagonist) therapy. The INR is calculated as the patient PT divided by the mean normal PT, raised to the power of the international sensitivity index (ISI) of the thromboplastin reagent. It does not measure heparin levels, platelet function, or the intrinsic pathway; heparin is monitored with the aPTT or anti-Xa assay, not the INR.
- A patient with a lifelong history of mucocutaneous bleeding has a normal platelet count, a borderline prolonged aPTT, and a normal PT. Workup shows a decreased VWF antigen, a decreased ristocetin cofactor activity, and a mildly decreased factor VIII. Which diagnosis best fits this pattern?
- Antithrombin deficiency
- Von Willebrand disease
- Immune thrombocytopenia
- Factor VII deficiency
Correct answer: Von Willebrand disease
Von Willebrand disease best fits a decreased VWF antigen, decreased ristocetin cofactor (VWF activity), and a secondarily reduced factor VIII. Von Willebrand factor carries and stabilizes factor VIII in plasma, so a quantitative VWF deficiency lowers factor VIII and can mildly prolong the aPTT while the PT stays normal. The ristocetin cofactor assay reflects VWF function because ristocetin promotes VWF binding to platelet glycoprotein Ib. Immune thrombocytopenia lowers the platelet count, and factor VII deficiency prolongs the PT, so neither matches this picture.
- A medical laboratory scientist is explaining why a patient can have a prolonged aPTT with a normal PT. Which deficiency would produce this pattern?
- Factor VII deficiency
- Factor VIII deficiency
- Combined factor V and prothrombin deficiency
- Fibrinogen deficiency
Correct answer: Factor VIII deficiency
Factor VIII deficiency produces a prolonged aPTT with a normal PT because factor VIII is part of the intrinsic pathway measured by the aPTT and is not assessed by the PT. The aPTT evaluates the intrinsic and common pathways (factors XII, XI, IX, VIII, X, V, II, and fibrinogen), while the PT evaluates the extrinsic and common pathways (factor VII plus the common factors). An isolated factor VII deficiency would instead prolong the PT with a normal aPTT, and deficiencies of common-pathway components such as fibrinogen or prothrombin would prolong both tests.
- A patient on continuous intravenous unfractionated heparin needs therapy monitored. Which laboratory approach is most appropriate, and what is the conventional target?
- Follow the platelet count alone, targeting greater than 150×109/L
- Follow the PT/INR, targeting an INR of 2.0 to 3.0
- Follow the thrombin time, targeting a value below the reference range
- Follow the aPTT, targeting roughly 1.5 to 2.5 times the control value (correlated to anti-Xa 0.3 to 0.7 IU/mL)
Correct answer: Follow the aPTT, targeting roughly 1.5 to 2.5 times the control value (correlated to anti-Xa 0.3 to 0.7 IU/mL)
Monitoring unfractionated heparin is done with the aPTT, conventionally targeting about 1.5 to 2.5 times the control value, a range each laboratory calibrates against an anti-Xa heparin activity of roughly 0.3 to 0.7 IU/mL. Heparin potentiates antithrombin and inhibits thrombin and factor Xa, prolonging the intrinsic-pathway aPTT. The PT/INR is used for warfarin, not heparin, and platelet counts or an isolated thrombin time are not the standard tools for titrating a heparin infusion.
- A patient presents with a prolonged aPTT. A 1:1 mixing study with normal pooled plasma fully corrects the aPTT into the reference range. What does this mixing study result most strongly suggest?
- A lupus anticoagulant
- The presence of a specific factor VIII inhibitor
- A coagulation factor deficiency rather than an inhibitor
- Active disseminated intravascular coagulation
Correct answer: A coagulation factor deficiency rather than an inhibitor
Correction of a prolonged aPTT after a 1:1 mix with normal plasma most strongly suggests a coagulation factor deficiency rather than an inhibitor. Normal plasma supplies roughly 50 percent of each factor, which is enough to normalize the clotting time when the only problem is a missing or low factor. If an inhibitor such as a specific factor antibody or a lupus anticoagulant were present, the mix would fail to correct because the inhibitor also acts on the added normal plasma.
- A direct antiglobulin test (DAT) is ordered on a newborn with jaundice. What does this test actually demonstrate when it is positive?
- That the patient's own red cells are already coated in vivo with antibody and/or complement
- That the patient's plasma contains free, unbound antibody capable of reacting with reagent red cells
- That the ABO forward and reverse groupings disagree
- That the patient lacks the H antigen on the red cell surface
Correct answer: That the patient's own red cells are already coated in vivo with antibody and/or complement
A positive DAT demonstrates that the patient's own red cells are already coated in vivo with IgG antibody and/or complement (C3). Anti-human globulin reagent is added directly to washed patient cells, so it detects sensitization that has already occurred in the body, as in hemolytic disease of the newborn, autoimmune hemolytic anemia, or a transfusion reaction. Detecting free unbound antibody in plasma describes the indirect antiglobulin test (IAT), not the DAT.
- A laboratory needs to determine whether a patient has formed an antibody against transfused donor cells, where the antibody is still circulating freely in the plasma. Which test detects antibody that is free in the plasma rather than already bound to red cells in vivo?
- Indirect antiglobulin test (IAT)
- Direct antiglobulin test (DAT)
- Forward ABO grouping
- Anti-H lectin test
Correct answer: Indirect antiglobulin test (IAT)
The indirect antiglobulin test (IAT) detects antibody that is free in the plasma. In the IAT, patient plasma is incubated with reagent red cells in vitro, then anti-human globulin is added to detect any antibody that attached during incubation; it is the basis of antibody screening, antibody identification, and the antiglobulin crossmatch. The direct antiglobulin test (DAT), by contrast, detects antibody already bound to the patient's cells in vivo and requires no incubation step.
- A patient's red cells fail to react with anti-A, anti-B, and anti-A,B, suggesting group O, yet the serum agglutinates group O reagent red cells along with A1 and B cells. Anti-H lectin (Ulex europaeus) does NOT agglutinate the patient's cells. Which phenotype best explains these findings?
- Subgroup A2 with anti-A1
- Group O, Rh-negative
- Group AB with acquired B antigen
- Bombay phenotype (Oh)
Correct answer: Bombay phenotype (Oh)
The Bombay phenotype (Oh) explains these findings. Bombay individuals are homozygous for an inactive FUT1 gene (hh) and cannot make H antigen, so their cells carry no A, B, or H and do not react with anti-H lectin. Because they lack H, they produce a potent anti-H (plus anti-A and anti-B) that agglutinates all ordinary group O cells, which are rich in H. A true group O person would type as O but their cells would react strongly with anti-H lectin, ruling that out.
- Forward grouping shows a patient is group A (cells react with anti-A only). Reverse grouping shows agglutination with both A1 cells and B cells. The patient is otherwise healthy with no recent transfusion. What is the most likely explanation and confirmatory step?
- Acquired B antigen; confirm by lowering the anti-B reagent pH
- Cold autoantibody; confirm by warming the sample to 37 C
- Subgroup A2 (or weaker) with anti-A1; test the patient's cells with Dolichos biflorus lectin
- Rouleaux; confirm with a saline replacement technique
Correct answer: Subgroup A2 (or weaker) with anti-A1; test the patient's cells with Dolichos biflorus lectin
The likely explanation is a subgroup such as A2 that has formed anti-A1, confirmed by testing the patient's cells with Dolichos biflorus lectin. Anti-A1 is a naturally occurring antibody seen in some A2 and weaker A subgroups; it reacts with the A1 reagent cells in the reverse grouping, producing an unexpected reaction. Dolichos biflorus lectin agglutinates A1 cells but not A2 cells, so a negative lectin result on the patient's cells confirms a subgroup of A.
- Which statement best defines an ABO discrepancy?
- A weak D result that requires antiglobulin-phase testing
- A mismatch between the antigens detected on the red cells (forward typing) and the antibodies detected in the serum (reverse typing)
- A difference between the patient's ABO group and the ABO group of the intended donor unit
- Any positive antibody screen in a group O patient
Correct answer: A mismatch between the antigens detected on the red cells (forward typing) and the antibodies detected in the serum (reverse typing)
An ABO discrepancy is a mismatch between the antigens detected on the red cells (forward typing) and the antibodies detected in the serum (reverse typing). Because Landsteiner's rule predicts that the two should always agree, any disagreement, whether from a missing/extra cell reaction or a missing/extra serum reaction, must be investigated and resolved before the ABO group is reported. A patient-versus-donor mismatch is a compatibility issue, not an ABO discrepancy in the typing sense.
- Landsteiner's rule is used to validate routine ABO testing. Which serum finding would a technologist expect from a person whose red cells type as group B?
- Neither anti-A nor anti-B in the serum
- Anti-A in the serum
- Both anti-A and anti-B in the serum
- Anti-B in the serum
Correct answer: Anti-A in the serum
A group B individual is expected to have anti-A in the serum. Landsteiner's rule states that healthy individuals produce isoagglutinins against the ABO antigen(s) they lack, so a group B person, lacking the A antigen, makes anti-A. This expected reciprocal relationship is why reverse (serum) grouping serves as a built-in check on forward (cell) grouping.
- An Rh-negative pregnant patient with no anti-D detected is seen for routine prenatal care. According to standard prophylaxis practice, when is a 300-microgram antepartum dose of Rh immune globulin (RhIG) routinely given?
- At approximately 28 weeks of gestation
- Only if the antibody screen becomes positive
- At the first prenatal visit regardless of gestational age
- Only after delivery if the infant is D-positive
Correct answer: At approximately 28 weeks of gestation
A 300-microgram antepartum dose of RhIG is routinely given at approximately 28 weeks of gestation to a D-negative, unsensitized patient. This timing covers silent third-trimester fetomaternal hemorrhage; a second dose is then given within 72 hours postpartum if the infant is confirmed D-positive. Giving it only after delivery would miss antenatal sensitization, and RhIG is withheld (not started) once a patient has already formed active anti-D.
- Besides the routine 28-week and postpartum doses, which additional event is a recognized indication for administering Rh immune globulin to a D-negative, unsensitized pregnant patient?
- Amniocentesis or abdominal trauma during pregnancy
- A group O blood type in the mother
- A positive rubella titer
- Maternal iron-deficiency anemia
Correct answer: Amniocentesis or abdominal trauma during pregnancy
Amniocentesis or abdominal trauma is a recognized indication for RhIG because either can cause fetomaternal hemorrhage that exposes the mother to fetal D-positive cells. Other potentially sensitizing events include chorionic villus sampling, ectopic pregnancy, threatened or spontaneous abortion, and external cephalic version. A rubella titer, iron-deficiency anemia, and maternal blood group are unrelated to D alloimmunization risk.
- A donor unit types as D-negative when tested by immediate-spin with anti-D. Why must the unit then undergo weak D testing (an antiglobulin-phase test for weak D) before it can be labeled?
- Because a weakly expressed D antigen can immunize a D-negative recipient, so such units must be labeled D-positive
- To confirm the unit is free of clinically significant alloantibodies
- Because weak D testing detects the H antigen needed for ABO labeling
- To distinguish A1 from A2 subgroups in the donor
Correct answer: Because a weakly expressed D antigen can immunize a D-negative recipient, so such units must be labeled D-positive
Weak D testing is required on donor units because a weakly expressed D antigen can still immunize a D-negative recipient, so any unit positive for weak D must be labeled D-positive. The procedure incubates the cells with anti-D and adds anti-human globulin to detect low-level D expression missed at immediate spin. This donor requirement contrasts with recipients, where weak D individuals can usually be transfused as if D-negative; weak D testing does not assess alloantibodies, ABO subgroups, or H antigen.
- A pretransfusion antibody screen is positive at the antiglobulin phase with a negative autocontrol. What is the appropriate next step and its purpose?
- Perform a direct antiglobulin test to detect in vivo sensitization
- Repeat the ABO forward and reverse grouping to resolve a discrepancy
- Issue the negative-autocontrol units as compatible without further testing
- Perform an antibody identification panel to determine the specificity of the alloantibody
Correct answer: Perform an antibody identification panel to determine the specificity of the alloantibody
The next step is to perform an antibody identification panel to determine the specificity of the detected alloantibody. The antibody screen only tells you that a clinically significant antibody is present (a yes/no result using 2 to 3 group O screening cells); the identification panel tests the plasma against a larger set of group O reagent cells (at least eight) with known antigen profiles so the exact specificity can be deduced and antigen-negative units selected. The negative autocontrol points to an alloantibody rather than an autoantibody.
- A patient receiving a unit of red cells develops a temperature rise of 1.2 degrees C (to 38.5 degrees C) with chills about 45 minutes into the transfusion, but has no back pain, no hemoglobinuria, and a normal blood pressure. The post-transfusion specimen shows no hemolysis and the clerical check and DAT are negative. Which reaction is most consistent with these findings?
- Anaphylactic reaction
- Febrile nonhemolytic transfusion reaction
- Transfusion-associated circulatory overload
- Acute hemolytic transfusion reaction
Correct answer: Febrile nonhemolytic transfusion reaction
A febrile nonhemolytic transfusion reaction (FNHTR) is the correct fit. By AABB definition it is a temperature rise of at least 1 degree C to 38 degrees C or higher (and/or chills/rigors) during or within 4 hours of transfusion, with no evidence of hemolysis and a negative workup. It is driven by recipient antibodies against donor leukocytes or by cytokines that accumulate in stored cellular components. An acute hemolytic reaction would show hemoglobinuria and a positive DAT, and TACO causes respiratory distress from volume overload rather than isolated fever.
- A blood bank wants to reduce the incidence of febrile nonhemolytic transfusion reactions to platelets and red cells. Which intervention most directly addresses the usual cause of these reactions?
- Washing all units to remove plasma proteins
- Prestorage leukoreduction of cellular components
- Premedicating every recipient with antihistamine
- Irradiating all cellular components
Correct answer: Prestorage leukoreduction of cellular components
Prestorage leukoreduction is the most direct preventive measure. Because FNHTRs are caused by recipient anti-leukocyte antibodies reacting with residual donor white cells and by cytokines that leukocytes release into the unit during storage, removing white cells before storage limits both mechanisms. Irradiation prevents transfusion-associated graft-versus-host disease, washing reduces allergic reactions to plasma proteins, and antihistamines target allergic (not febrile) reactions.
- Five days after a red cell transfusion, a previously transfused patient shows an unexplained fall in hemoglobin, a rising bilirubin, a newly positive direct antiglobulin test, and a positive antibody screen that was negative at the time of crossmatch. Which transfusion reaction does this pattern represent?
- Acute hemolytic transfusion reaction
- Transfusion-related acute lung injury
- Febrile nonhemolytic transfusion reaction
- Delayed hemolytic transfusion reaction
Correct answer: Delayed hemolytic transfusion reaction
A delayed hemolytic transfusion reaction is the answer. It occurs days to weeks after transfusion when an anamnestic (memory) antibody response raises the titer of a previously formed alloantibody that had fallen below detectable levels at crossmatch. The result is extravascular destruction of transfused cells, an unexpected hemoglobin drop, rising indirect bilirubin, and a newly positive DAT and antibody screen. An acute hemolytic reaction occurs within hours and is usually intravascular.
- Which antibody specificities are classically implicated in delayed hemolytic transfusion reactions because their corresponding antibodies fall to undetectable levels between exposures?
- Anti-Lewis a and anti-Lewis b
- Antibodies in the Kidd and Rh systems such as anti-Jka and anti-E
- Anti-I and anti-H
- Anti-A and anti-B
Correct answer: Antibodies in the Kidd and Rh systems such as anti-Jka and anti-E
Kidd and Rh system antibodies such as anti-Jka and anti-E are the classic culprits. Kidd antibodies in particular are notorious for declining below the detection threshold over time, so they evade the antibody screen at crossmatch and then mount a brisk anamnestic response after re-exposure, producing delayed hemolysis. ABO antibodies cause immediate intravascular reactions, while Lewis and anti-I/anti-H are cold-reacting and generally not associated with delayed hemolysis.
- Within minutes of starting a red cell transfusion, a patient develops fever, chills, severe lower back and flank pain, hypotension, and red-tinged urine. Which set of signs is most characteristic of an acute hemolytic transfusion reaction?
- Isolated low-grade fever that resolves spontaneously
- Dyspnea with hypertension and jugular venous distension
- Fever, back/flank pain, hypotension, and hemoglobinuria
- Urticaria and pruritus with normal vital signs
Correct answer: Fever, back/flank pain, hypotension, and hemoglobinuria
Fever and chills with back or flank pain, hypotension, and hemoglobinuria are the hallmark signs of an acute hemolytic transfusion reaction. Rapid intravascular destruction of incompatible donor cells releases free hemoglobin (causing hemoglobinemia and hemoglobinuria) and triggers cytokine release, which can progress to shock, disseminated intravascular coagulation, and acute renal failure. Urticaria alone suggests an allergic reaction, and dyspnea with hypertension and jugular distension points to circulatory overload.
- A nurse calls the blood bank because a patient developed back pain and dark urine shortly after a transfusion began. After stopping the transfusion and providing supportive care, what is the most appropriate FIRST laboratory step in the reaction investigation?
- Perform a clerical check and visually inspect the post-transfusion plasma for hemolysis
- Order a peripheral blood smear for schistocytes
- Repeat the antibody panel on the donor unit
- Send the unit for bacterial culture before anything else
Correct answer: Perform a clerical check and visually inspect the post-transfusion plasma for hemolysis
Performing a clerical check and visually inspecting the post-transfusion plasma for hemoglobinemia is the correct first step. The clerical check confirms the right unit went to the right patient, since ABO-incompatible acute hemolytic reactions are most often caused by misidentification. Comparing pre- and post-transfusion plasma for a pink or red discoloration rapidly screens for intravascular hemolysis and guides whether a full serologic workup and DAT are needed.
- What is the underlying immunologic cause of hemolytic disease of the fetus and newborn (HDFN)?
- Maternal IgM antibodies agglutinating fetal cells in the placenta
- Maternal IgG antibodies crossing the placenta and destroying fetal red cells bearing a paternally inherited antigen
- Fetal antibodies attacking maternal red cells
- Complement deposited directly on the placenta by the fetus
Correct answer: Maternal IgG antibodies crossing the placenta and destroying fetal red cells bearing a paternally inherited antigen
HDFN is caused by maternal IgG antibodies that cross the placenta and bind fetal red cells carrying a paternally inherited antigen the mother lacks, leading to their destruction in the fetal spleen. Only IgG crosses the placenta, which is why IgM antibodies (such as the naturally occurring anti-A and anti-B isoagglutinins in their IgM form) do not cause classic HDFN. Anti-D remains the most clinically severe cause, while ABO incompatibility is the most common but usually mild.
- Compared with anti-D HDFN, ABO hemolytic disease of the newborn most characteristically:
- Is prevented by Rh immune globulin
- Requires prior maternal sensitization and spares the first pregnancy
- Always causes hydrops fetalis
- Can affect a first pregnancy and usually follows a milder clinical course
Correct answer: Can affect a first pregnancy and usually follows a milder clinical course
ABO HDFN can affect a first pregnancy and is usually mild. Group O mothers naturally possess IgG anti-A,B without prior pregnancy or transfusion, so the first ABO-incompatible fetus can be affected, but fetal A and B antigens are weakly expressed and widely distributed, which limits hemolysis. Anti-D HDFN, in contrast, generally requires prior sensitization (sparing the first pregnancy), can be severe enough to cause hydrops, and is the form prevented by Rh immune globulin.
- A blood bank must select red cells for an intrauterine or neonatal exchange transfusion in a case of anti-D HDFN. Which unit characteristic is essential to prevent further hemolysis of the infant's cells?
- Units that are the oldest available to conserve fresh inventory
- Units that are unwashed whole blood
- Units that are D-positive to match the father
- Units that are D-negative and lack the antigen corresponding to the maternal antibody
Correct answer: Units that are D-negative and lack the antigen corresponding to the maternal antibody
The cells must be D-negative and negative for the antigen that the maternal antibody targets. Because maternal anti-D crosses into the infant and would destroy any D-positive cells, transfused red cells must lack D (and any other implicated antigen) so they are not hemolyzed. For exchange or intrauterine transfusion these units are also typically group O, fresh, CMV-reduced-risk, and irradiated to prevent graft-versus-host disease.
- During a red cell transfusion an immunocompromised patient develops acute respiratory distress, bilateral pulmonary infiltrates, and hypoxemia within 4 hours, but has a normal central venous pressure and no jugular venous distension. Which reaction best fits this presentation?
- Allergic transfusion reaction
- Transfusion-associated circulatory overload (TACO)
- Delayed hemolytic transfusion reaction
- Transfusion-related acute lung injury (TRALI)
Correct answer: Transfusion-related acute lung injury (TRALI)
Transfusion-related acute lung injury (TRALI) is the best fit. TRALI is noncardiogenic (permeability) pulmonary edema occurring within 6 hours of transfusion, typically with normal central venous pressure and no signs of fluid overload. It is associated with donor anti-leukocyte (anti-HLA or anti-neutrophil) antibodies. TACO, by contrast, is hydrostatic edema with hypertension, jugular venous distension, and an elevated BNP, and it responds to diuretics.
- An elderly patient with congestive heart failure becomes acutely dyspneic and hypertensive with distended neck veins about 90 minutes into a unit of red cells, and an NT-proBNP drawn afterward is markedly elevated. Which transfusion complication is most likely?
- Febrile nonhemolytic reaction
- Transfusion-associated circulatory overload
- Bacterial sepsis from the unit
- Transfusion-related acute lung injury
Correct answer: Transfusion-associated circulatory overload
Transfusion-associated circulatory overload (TACO) is most likely. TACO is hydrostatic pulmonary edema from volume overload and presents with dyspnea, hypertension, jugular venous distension, and a rise in BNP or NT-proBNP, often improving with diuretics. Risk is highest in patients with cardiac or renal impairment and at the extremes of age. TRALI is distinguished by hypotension and the absence of circulatory overload signs.
- Which transfusion complication is specifically prevented by gamma or X-ray irradiation of cellular blood components?
- Febrile nonhemolytic transfusion reaction
- ABO-incompatible hemolysis
- Transfusion-associated graft-versus-host disease
- Iron overload
Correct answer: Transfusion-associated graft-versus-host disease
Irradiation prevents transfusion-associated graft-versus-host disease (TA-GVHD). Irradiation inactivates donor T lymphocytes so they cannot engraft and attack the recipient's tissues, a complication that is highly lethal in immunocompromised patients and in directed donations from blood relatives. Leukoreduction reduces febrile reactions, iron overload relates to chronic transfusion burden, and ABO hemolysis is prevented by correct typing and crossmatching.
- A patient with a documented history of recurrent allergic urticarial reactions to transfusion, and another with confirmed IgA deficiency and anti-IgA antibodies, both need red cells. Which modification best addresses the plasma-protein basis of their reactions?
- Frozen-thawed glycerolized red cells issued without further processing
- Irradiated red cells
- CMV-seronegative red cells
- Washed red cells
Correct answer: Washed red cells
Washed red cells are the appropriate choice. Washing removes residual donor plasma, which carries the proteins (including IgA) responsible for allergic and anaphylactic reactions, making washed units suitable for patients with severe recurrent allergic reactions or IgA deficiency with anti-IgA. Irradiation targets GVHD and CMV-seronegative units reduce CMV transmission, neither of which removes the offending plasma proteins.
- A unit of platelets stored at room temperature is the most likely cellular component to transmit bacterial contamination and cause a septic transfusion reaction. Which feature of platelet storage explains this elevated risk?
- Platelets contain no plasma, so bacteria are concentrated
- Platelets are stored frozen, which promotes bacterial growth on thawing
- Platelets are stored at 20 to 24 degrees C with agitation, conditions that favor bacterial proliferation
- Platelets are stored at 1 to 6 degrees C, which selects for cold-tolerant bacteria
Correct answer: Platelets are stored at 20 to 24 degrees C with agitation, conditions that favor bacterial proliferation
Platelets are stored at room temperature, 20 to 24 degrees C, with continuous agitation, and this warm environment allows any contaminating bacteria to multiply, making platelets the cellular product most often implicated in septic transfusion reactions. Red cells are refrigerated at 1 to 6 degrees C, which slows most bacterial growth. Blood banks mitigate platelet sepsis risk through bacterial detection testing or pathogen reduction.
