- Levey-Jennings chart
- A QC chart plotting daily control values against the established mean and SD limits to monitor an analytical method over time.
- Random error
- Unpredictable scatter of control values around the mean that reduces precision, with no consistent direction.
- Systematic error
- A consistent bias (trend or shift) in control values that reduces accuracy; from a calibration, reagent, or instrument problem.
- Westgard 1-3s rule
- Rejects a run when a single control value exceeds the mean by more than 3 SD; flags random (and gross) error.
- Westgard 2-2s rule
- Two consecutive control values both exceed the same 2 SD limit; indicates systematic error.
- Trend (Levey-Jennings)
- A gradual drift of controls in one direction over several runs; suggests a deteriorating reagent or aging lamp (systematic error).
- Shift (Levey-Jennings)
- An abrupt jump of controls to a new level that persists; suggests a new reagent lot, recalibration, or maintenance.
- Accuracy
- How close a measured value is to the true value.
- Precision
- How reproducible repeated measurements of the same sample are.
- Coefficient of variation (CV)
- A measure of precision: (standard deviation / mean) x 100, expressed as a percentage; lower is more precise.
- Beer's law
- Absorbance is directly proportional to analyte concentration and the light-path length in spectrophotometry.
- Delta check
- A check comparing a patient's current result with that same patient's previous result for the same analyte, to flag possible errors.
- Critical (panic) value
- A life-threatening result that must be reported immediately to a caregiver with a documented read-back.
- CLSI order of draw
- Blood cultures, sodium citrate, serum, heparin, EDTA, then fluoride; prevents additive carryover between tubes.
- Citrate before EDTA
- The high-yield order-of-draw rule: EDTA carryover chelates calcium and falsely prolongs coagulation results.
- Serum
- The liquid portion of clotted blood; lacks fibrinogen and clotting factors.
- Plasma
- The liquid portion of anticoagulated blood; still contains fibrinogen and clotting factors.
- EDTA (lavender tube)
- Anticoagulant that chelates calcium; the routine tube for the CBC.
- Standard (universal) precautions
- Treating every patient specimen as potentially infectious — the basis of laboratory safety.
- Biosafety level 2 (BSL-2)
- The containment level appropriate for routine clinical laboratory work with most bloodborne pathogens.
- Safety Data Sheet (SDS)
- The document giving handling and storage information for a hazardous chemical.
- Class C fire extinguisher
- The extinguisher appropriate for an electrical fire in the laboratory.
- CLIA
- The U.S. federal regulation governing quality standards for all clinical laboratory testing.
- Polymerase chain reaction (PCR)
- Amplifies a target DNA sequence through repeated cycles of denaturation, annealing, and extension.
- Taq polymerase
- The heat-stable enzyme that synthesizes new DNA strands during PCR.
- RT-PCR
- Reverse-transcriptase PCR — used when the starting template is RNA, first converting it to cDNA.
- Real-time (quantitative) PCR
- Monitors amplification continuously using fluorescence rather than an end-point gel.
- Gel electrophoresis
- Separates nucleic-acid or protein fragments by size using an electric field through a gel.
- Sensitivity (of a test)
- The ability to correctly identify those with disease; a highly sensitive test is good for screening (few false negatives).
- Chain of custody
- A continuous written record of specimen possession and handling for legal defensibility (forensic testing).
- Anion gap
- Sodium minus the sum of chloride and bicarbonate; estimates unmeasured anions to classify metabolic acidosis.
- Low anion gap
- Most often caused by hypoalbuminemia, since albumin is the major unmeasured anion.
- Bicarbonate buffer system
- The principal buffer of the extracellular fluid (bicarbonate / carbonic acid).
- Metabolic acidosis
- Low pH with low bicarbonate; respiratory compensation lowers pCO2 (hyperventilation).
- Ion-selective electrode (ISE)
- The reference method for measuring sodium and potassium; responds to the activity of the ion.
- Osmolal gap
- Measured minus calculated osmolality; an increased gap suggests a low-molecular-weight toxin (methanol, ethylene glycol).
- BUN/creatinine ratio > 20:1
- Suggests prerenal azotemia rather than intrinsic renal failure.
- Creatinine clearance
- An estimate of the glomerular filtration rate (GFR).
- Albumin-to-creatinine ratio (ACR)
- Screens for early diabetic glomerular damage; creatinine correction compensates for urine dilution.
- Troponin I/T
- Cardiac-specific structural protein; a rising-and-falling pattern is diagnostic of acute myocardial injury.
- Lipase
- The enzyme most specific for acute pancreatitis when interpreted with clinical findings.
- Obstructive (post-hepatic) jaundice
- Elevated direct (conjugated) bilirubin with elevated alkaline phosphatase and dark urine.
- Alkaline phosphatase (high, normal GGT)
- In a growing adolescent, most likely of bone origin rather than liver.
- C-reactive protein (CRP)
- An acute-phase reactant that rises rapidly with inflammation.
- Monoclonal gammopathy
- A sharp homogeneous spike in the gamma region on serum protein electrophoresis.
- Hexokinase glucose method
- The reference glucose method; glucose-6-phosphate dehydrogenase generates the measured NADPH.
- Hemoglobin A1c
- Glycated hemoglobin reflecting average blood glucose over the prior 2 to 3 months; reported as a percentage.
- Friedewald equation
- Estimates LDL = total cholesterol - HDL - (triglycerides / 5), mg/dL, fasting; unreliable at very high triglycerides.
- Primary hypothyroidism
- High TSH with low free T4.
- Alpha-fetoprotein (AFP)
- A marker for germ cell tumors that is also elevated in pregnancy.
- Spurious hyperkalemia
- Falsely elevated potassium, most commonly from hemolysis (potassium leaks from red cells) or delayed centrifugation.
- Lipemia interference
- A grossly lipemic specimen most affects spectrophotometric assays such as total bilirubin.
- Mean corpuscular volume (MCV)
- The average red-cell volume; classifies anemia as microcytic, normocytic, or macrocytic.
- Red cell distribution width (RDW)
- A measure of variation in red-cell size (anisocytosis); a high RDW means greater size variability.
- Iron deficiency anemia
- The most common microcytic, hypochromic anemia worldwide; serum ferritin is low.
- Ferritin
- The major iron-storage protein and an acute-phase reactant; low in iron deficiency, normal-to-high in chronic disease.
- Thalassemia trait
- Microcytic, hypochromic anemia with normal-to-elevated ferritin and an elevated RBC count.
- Megaloblastic anemia
- Macrocytic anemia from B12 or folate deficiency; hypersegmented neutrophils and oval macrocytes.
- Reticulocyte
- A young red blood cell; the count reflects marrow red-cell production and is stained with new methylene blue.
- Impedance (Coulter) principle
- Automated counting based on the change in electrical resistance as a cell passes through an aperture.
- Howell-Jolly bodies
- Nuclear remnant inclusions in red cells associated with asplenia or splenic hypofunction.
- Heinz bodies
- Inclusions of denatured hemoglobin seen in G6PD deficiency after oxidative stress.
- Basophilic stippling
- Coarse aggregated ribosomal RNA in red cells; classically associated with lead poisoning.
- Target cells
- Red cells with a central bullseye; seen in liver disease and hemoglobinopathies.
- Schistocytes
- Fragmented red cells seen with thrombocytopenia and high LDH in microangiopathic hemolytic anemia.
- Tear-drop cells (dacrocytes)
- Teardrop-shaped red cells with a leukoerythroblastic picture, suggesting myelofibrosis or marrow infiltration.
- Auer rods
- Needle-like cytoplasmic inclusions in myeloid blasts; diagnostic of a myeloid lineage (acute myeloid leukemia).
- Smudge cells
- Fragile lymphocytes that rupture on smear, accompanying chronic lymphocytic leukemia.
- Philadelphia chromosome t(9;22)
- The cytogenetic hallmark of chronic myelogenous leukemia.
- Toxic granulation / Dohle bodies / left shift
- Neutrophil changes consistent with severe bacterial infection or sepsis.
- Hemoglobin S (sickle cell)
- Results from valine replacing glutamic acid at position 6 of the beta-globin chain.
- Erythrocyte sedimentation rate (ESR)
- Most directly increased by elevated fibrinogen.
- New methylene blue
- The supravital stain used to demonstrate reticulocytes.
- Buffy coat
- The layer in centrifuged anticoagulated blood containing white blood cells and platelets.
- Osmotic fragility test
- Increased fragility from decreased surface-to-volume ratio, as in hereditary spherocytosis.
- Prothrombin time (PT)
- Assesses the extrinsic and common pathways; sensitive to factor VII; reported as INR to monitor warfarin.
- Activated partial thromboplastin time (aPTT)
- Assesses the intrinsic and common pathways; used to monitor unfractionated heparin.
- International normalized ratio (INR)
- Standardizes the PT across thromboplastin reagents and labs to monitor warfarin therapy.
- Mixing study (1:1)
- Corrects = factor deficiency; does not correct = inhibitor (e.g., lupus anticoagulant).
- Lupus anticoagulant
- An inhibitor that prolongs the aPTT in vitro (no correction on mixing) but is associated with thrombosis.
- D-dimer
- A fibrin degradation product; sensitive but not specific for clot formation and lysis (good rule-out).
- Disseminated intravascular coagulation (DIC)
- Elevated D-dimer with prolonged PT and PTT, low fibrinogen, and thrombocytopenia.
- Sodium citrate (3.2%) tube
- The reference anticoagulant for coagulation testing; collected at a 9:1 blood-to-citrate ratio.
- Factor VII deficiency
- Suggested by a prolonged PT with a normal aPTT (extrinsic pathway).
- Factor VIII deficiency (hemophilia A)
- Prolonged aPTT with a normal PT, reflecting an intrinsic-pathway factor.
- Von Willebrand disease
- Lifelong mucocutaneous bleeding with normal platelet count and a borderline/prolonged aPTT (reduced factor VIII).
- Cryoprecipitate
- The component of choice to raise fibrinogen in a bleeding patient with hypofibrinogenemia.
- IgM
- The first immunoglobulin produced in a primary immune response; a strong agglutinator.
- IgG
- The most abundant serum immunoglobulin; dominates the secondary response and crosses the placenta.
- IgA
- The immunoglobulin predominating in secretions such as saliva, tears, and breast milk.
- IgE
- The immunoglobulin mediating type I immediate hypersensitivity (allergy).
- Classical complement pathway
- An antibody-dependent cascade triggered when IgG or IgM bound to antigen is recognized by C1q.
- ELISA
- An enzyme-labeled antibody plus a substrate produces a measurable color to detect antigen or antibody.
- Prozone phenomenon
- A false-negative agglutination caused by antibody excess relative to antigen; resolved by diluting the serum.
- Fourfold rise in titer
- A rise between acute and convalescent sera indicating recent or current infection.
- Anti-HBs positive, anti-HBc negative
- Immunity to hepatitis B from vaccination (anti-HBc appears only with natural infection).
- HBsAg with IgM anti-HBc
- Indicates acute hepatitis B infection.
- Heterophile (Monospot) test
- Supports a diagnosis of infectious mononucleosis (EBV).
- RPR confirmed by FTA-ABS
- A positive nontreponemal screen confirmed by a treponemal test indicates active or past syphilis.
- Antinuclear antibody (ANA)
- A screening test most commonly used in the evaluation of systemic lupus erythematosus.
- Rheumatoid factor
- An autoantibody, usually IgM, directed against the Fc portion of IgG.
- CD4 T-lymphocyte count
- Used to monitor HIV disease progression and immune status.
- HIV confirmatory testing
- A repeatedly reactive HIV screen is confirmed by an antibody-differentiation assay (historically Western blot).
- Forward grouping
- ABO testing of red cells with anti-A and anti-B reagents to detect A and B antigens.
- Reverse grouping
- ABO testing of serum against known A1 and B cells to detect ABO antibodies.
- Landsteiner's rule
- A person has the ABO antibody directed against the A or B antigen they lack.
- ABO discrepancy
- A mismatch between the antigens detected on the cells (forward) and the antibodies in the serum (reverse).
- Group O (universal red-cell donor)
- Lacks A and B antigens; O-negative units are used for emergency red-cell transfusion.
- Group AB (universal red-cell recipient)
- Plasma contains neither anti-A nor anti-B.
- Direct antiglobulin test (DAT)
- Detects antibody or complement already bound to a patient's red cells in vivo.
- Indirect antiglobulin test (IAT)
- Detects antibodies in the patient's serum in vitro; used for antibody screening and crossmatch.
- Check cells
- IgG-coated red cells added to a negative antiglobulin test to confirm the AHG reagent was added and active.
- Major crossmatch
- Tests compatibility between recipient serum and donor red cells.
- Rh immune globulin (RhIG)
- Anti-D given to an Rh-negative mother to prevent anti-D alloimmunization (around 28 weeks and after delivery).
- Anti-Jka (Kidd) dosage effect
- Reacts more strongly with homozygous cells; classically shows a dosage effect.
- Weak D (Du)
- A weakly expressed D antigen; such donors are typed and labeled Rh-positive.
- Bombay phenotype (Oh)
- Cells fail to react with anti-A, anti-B, and anti-A,B, yet the serum contains anti-A, anti-B, and anti-H.
- C antigen (Rh)
- The most immunogenic Rh antigen after D.
- Antibody identification panel
- Performed when an antibody screen is positive, to determine the specificity of the alloantibody.
- Acute hemolytic transfusion reaction (AHTR)
- ABO-incompatible red cells cause intravascular hemolysis; the most immediately fatal reaction.
- Febrile nonhemolytic transfusion reaction (FNHTR)
- A >=1 C temperature rise from anti-leukocyte antibodies or cytokines; the most common reaction.
- Leukoreduction
- Removal of leukocytes that prevents febrile nonhemolytic reactions, CMV transmission, and HLA alloimmunization.
- TRALI
- Transfusion-related acute lung injury — immune, non-cardiogenic pulmonary edema within 6 hours; a leading cause of transfusion death.
- TACO
- Transfusion-associated circulatory overload — volume overload causing dyspnea, hypertension, and cardiogenic edema.
- Delayed hemolytic transfusion reaction
- An anamnestic antibody response (e.g., Kidd, Rh) days after transfusion in a previously sensitized patient.
- Transfusion-associated graft-versus-host disease (TA-GVHD)
- Donor lymphocytes attack the host; prevented by gamma or X-ray irradiation of cellular components.
- Washed red cells
- The component for patients with recurrent severe allergic reactions or IgA deficiency.
- Hemolytic disease of the fetus and newborn (HDFN)
- Maternal IgG antibodies cross the placenta and destroy fetal red cells bearing a paternal antigen.
- ABO HDN vs anti-D HDFN
- ABO HDN can affect a first pregnancy and is usually milder than anti-D disease.
- Clerical check (suspected reaction)
- The first blood-bank step in a suspected reaction: verify identity and inspect post-transfusion plasma for hemolysis.
- Platelet bacterial contamination
- Platelets stored at 20 to 24 C with agitation are the cellular component most likely to transmit bacteria.
- Gram stain
- A differential stain classifying bacteria as Gram-positive (purple, thick peptidoglycan) or Gram-negative (pink, outer membrane).
- Catalase test
- Separates catalase-positive staphylococci from catalase-negative streptococci and enterococci.
- Coagulase test
- Detects an enzyme converting fibrinogen to fibrin; coagulase-positive identifies Staphylococcus aureus.
- Staphylococcus aureus
- Catalase-positive, coagulase-positive Gram-positive cocci in clusters.
- Streptococcus pyogenes (group A)
- Beta-hemolytic, bacitracin-sensitive, PYR-positive Gram-positive cocci in chains.
- Streptococcus pneumoniae
- Alpha-hemolytic, bile-soluble, optochin-sensitive Gram-positive diplococcus.
- Novobiocin test
- Differentiates novobiocin-sensitive S. epidermidis from novobiocin-resistant S. saprophyticus.
- Oxidase test
- Presumptively identifies organisms such as Pseudomonas aeruginosa (and Neisseria).
- MacConkey agar
- Selective and differential for Gram-negative enterics; strong lactose fermenters form pink-to-red colonies.
- Escherichia coli
- The most common cause of urinary tract infection; a lactose-fermenting, indole-positive enteric.
- Mannitol salt agar
- Selective and differential medium for staphylococci.
- Modified Thayer-Martin agar
- Selective medium for Neisseria gonorrhoeae.
- Acid-fast (Ziehl-Neelsen) stain
- Identifies Mycobacterium by its mycolic-acid cell wall.
- Kirby-Bauer disk diffusion
- Measures susceptibility by the diameter of the zone of inhibition compared to standardized breakpoints.
- Germ tube test
- Rapid presumptive identification of Candida albicans.
- Haemophilus influenzae
- Requires both X (hemin) and V (NAD) factors for growth.
- Helicobacter pylori
- A urease-positive curved Gram-negative rod associated with peptic ulcers and gastritis.
- Vibrio cholerae
- A curved, comma-shaped, oxidase-positive Gram-negative rod growing as yellow colonies on TCBS.
- Clostridioides difficile
- Causes antibiotic-associated pseudomembranous colitis; detected by toxin or molecular testing.
- Neisseria meningitidis
- A Gram-negative diplococcus from CSF that ferments both maltose and glucose.
- CAMP test
- Presumptively identifies group B Streptococcus (S. agalactiae).
- Cryptococcus neoformans
- An encapsulated yeast in CSF identified by India ink or cryptococcal antigen testing.
- RBC casts
- Red-cell casts in urine that specifically localize bleeding to the glomerulus (glomerulonephritis).
- Leukocyte esterase
- A urine dipstick reaction indicating white blood cells (neutrophils), supporting urinary tract infection.
- Nitrite (urine dipstick)
- A positive result suggests Gram-negative bacteria that reduce nitrate to nitrite.
- Urine protein pad
- Most sensitive to albumin; can miss non-albumin proteins such as Bence Jones.
- Glucose oxidase / peroxidase
- The enzyme system used by the urine reagent strip glucose test.
- Ketones (urine dipstick)
- React most strongly with acetoacetate.
- Calcium oxalate dihydrate crystals
- Envelope-shaped (octahedral) crystals in acidic-to-neutral urine; often a normal finding.
- Triple phosphate (struvite) crystals
- Coffin-lid-shaped crystals seen in alkaline urine.
- Cystine crystals
- Hexagonal urine crystals diagnostic of the inherited disorder cystinuria.
- Waxy casts
- Broad, high-refractive-index casts indicating chronic renal failure and urinary stasis.
- Isosthenuria
- A urine specific gravity fixed near 1.010 regardless of hydration; reflects renal tubular dysfunction.
- CSF in bacterial meningitis
- Decreased glucose, increased protein, and a neutrophil-predominant high cell count.
- Exudate
- A high-protein effusion (fluid-to-serum protein ratio > 0.5) from local inflammation.
- Monosodium urate crystals
- Negatively birefringent needle-shaped crystals in synovial fluid, diagnostic of gout.
- Chylous effusion
- A milky, triglyceride-rich body-fluid finding.
- Maltese cross (urine)
- Formation under polarized light indicating cholesterol or oval fat bodies (lipiduria).
- CSF cell-count tube
- The last tube collected (tube 3) is used for the cell count and differential to limit a traumatic-tap artifact.
