FREE ASCP MLS Study Guide 2026: A Complete Medical Lab Science Walkthrough

This free ASCP MLS study guide walks through the highest-yield content the ASCP Board of Certification Medical Laboratory Scientist (MLS) exam tests, organized by the seven content areas of the official ASCP BOC content guideline — Blood Banking, Urinalysis & Body Fluids, Chemistry, Hematology, Immunology, Microbiology, and Laboratory Operations.^[1]

It is interactive, not a wall of text: every content area has worked clinical scenarios, high-yield tables, labeled diagrams, and built-in flashcards, taught the way the MLS is actually tested — not just performing a test but interpreting the result and correlating it to disease, the baccalaureate-level skill that separates the MLS from the technician credential.

Read it content area by content area, then round out your prep with our practice questions and flashcards. The MLS is the bachelor-level scientist exam; if you are sitting the associate-level technician test, see our ASCP phlebotomy resources for the collection-focused credential — this guide is built to the broader, more advanced MLS(ASCP) content guideline.

ASCP MLS Exam Snapshot

Four content areas tie for largest — Blood Banking, Chemistry, Hematology, and Microbiology are each 17–22% of the exam, together roughly three-quarters of every question.^[1] Urinalysis & Body Fluids, Immunology, and Laboratory Operations are each 5–10%. So your study time should weight heavily toward the “big four” benches.

Percentages are each content area’s official weight range; the bars use a representative value within the range.^[1] This guide teaches all seven areas as seven study modules, so the structure matches the ASCP BOC content guideline exactly.

How the MLS Exam Is Built

The MLS exam follows the ASCP BOC content guideline (revised July 2023), which groups every item into seven content areas. The exam is delivered by computer adaptive testing: each correct answer raises the difficulty of the next item until you miss one, zeroing in on your true ability level. There is no set number of questions you must answer correctly — you pass if your final scaled score is above the pass point of 400.^[1][2]

• Blood Banking (17–22%) — blood products and donors, ABO/Rh and other blood-group systems, antibody detection and identification, compatibility testing, and transfusion practice.
• Chemistry (17–22%) — carbohydrates, lipids, proteins and enzymes, acid-base and electrolytes, endocrinology, therapeutic drug monitoring, and toxicology.
• Hematology (17–22%) — blood and marrow physiology, anemias and the leukemias, hemostasis and coagulation, and the laboratory tests that evaluate them.
• Microbiology (17–22%) — pre-analytic, analytic, and post-analytic procedures for bacteriology, plus mycobacteriology, virology, parasitology, and mycology.
• Urinalysis & Other Body Fluids (5–10%) — physical, chemical, and microscopic urinalysis and the analysis of CSF and other body fluids.
• Immunology (5–10%) — immune-system physiology, immune diseases, transplantation, and infectious-disease serology.
• Laboratory Operations (5–10%) — quality assessment, safety, laboratory mathematics, methodology and instrumentation, and management/education principles.

Questions come in two flavors: theoretical items that ask you to apply knowledge, perform calculations, and correlate results to a disease state, and procedural items that test techniques and quality assurance. Regulatory questions are based on U.S. sources such as AABB, FDA, and CLIA.^[1]

Blood Banking

Blood Banking (immunohematology) is 17–22% of the exam.^[1] It is the science of red cell antigens and antibodies, getting compatible blood to the patient safely, and recognizing when something goes wrong. Expect heavy emphasis on ABO/Rh, antibody work, the antiglobulin tests, and transfusion reactions.

Blood Products, Donors & Storage

Whole blood is separated into components, each stored differently. Packed red cellsare stored at 1–6°C for up to 42 days (with additive solution). Plateletsare stored at 20–24°C with continuous gentle agitation for up to 5–7 days — room temperature, never refrigerated, because cold damages them.

Fresh frozen plasma is frozen and thawed when needed. Cryoprecipitate concentrates fibrinogen, factor VIII, von Willebrand factor, and factor XIII.^[3]

ABO, Rh & Other Blood Groups

The ABO system is the most important in transfusion because the isoagglutinins (anti-A, anti-B) occur naturally — a person makes the antibody to the antigen they lack. Forward typingtests the patient’s red cells with anti-A and anti-B reagents; reverse typingtests the patient’s plasma against A1 and B reagent cells. The two must agree; a mismatch is an ABO discrepancy to resolve before any transfusion.^[3]

The Rh system is next in importance. The D antigen is the most immunogenic non-ABO antigen, so Rh-negative patients can readily form anti-D after exposure. Other systems matter for antibody work: Kell (anti-K causes severe HDFN and reactions), Kidd and Duffy (classic for the dosage effect and delayed reactions), Lewis (antigens adsorbed from plasma, not made by red cells), and the Bombay phenotype, which lacks the H precursor so no A, B, or H antigen forms.^[3]

Antibody Detection & Compatibility

Pretransfusion testing centers on the antibody screen and the crossmatch. The antibody screen tests the patient’s plasma against 2–3 reagent screening cells of known phenotype to detect clinically significant unexpected antibodies. If positive, an antibody panel identifies the specificity by matching the pattern of reactions to a single antigen profile (rule out the antigens on non-reactive cells).^[3]

The two antiglobulin (Coombs) tests are constantly tested. The DAT detects red cells already coated in vivo; the IAT detects in vitro sensitization after incubation. Both use anti-human globulin reagent.

When the antibody screen is negative and there is no antibody history, an abbreviated immediate-spin or electronic (computer) crossmatch is acceptable, because its only remaining job is to confirm ABO compatibility.^[3]

Transfusion Reactions & HDFN

The most dangerous reaction is the acute hemolytic transfusion reaction, almost always from an ABO mismatch due to clerical/identification error. Hallmarks are fever, flank pain, and hemoglobinemia (free hemoglobin in the post-transfusion plasma) — the most direct sign of intravascular hemolysis.

A febrile non-hemolytic reaction is a temperature rise of at least 1°C with chills and no hemolysis. A delayed hemolytic reaction appears days later, with a falling hemoglobin, a newly positive DAT, and a positive screen — an anamnestic antibody (often Kidd) rising after re-exposure.^[3]

Hemolytic disease of the fetus and newborn occurs when maternal IgG crosses the placenta and hemolyzes fetal red cells. The classic severe form is anti-D in a sensitized Rh-negative mother; ABO HDFN is more common but milder because most ABO antibodies are IgM and cannot cross the placenta. Rh immune globulin given to D-negative mothers prevents anti-D formation, and the Kleihauer-Betke test quantifies fetal red cells in maternal blood to calculate the RhIG dose.^[3][5]

Urinalysis & Body Fluids

Urinalysis and Other Body Fluids is 5–10% of the exam.^[1] It covers the physical, chemical, and microscopic examination of urine and the analysis of cerebrospinal, serous, and other body fluids — small in weight but rich in pattern-recognition questions.

Physical & Chemical Urinalysis

The physical exam records color, clarity, and specific gravity (concentration). The chemical exam is the reagent strip: pH, protein, glucose, ketones, blood, bilirubin, urobilinogen, nitrite, leukocyte esterase, and specific gravity. Know the interferences: high-dose ascorbic acid (vitamin C)can cause falsely low blood, glucose, and bilirubin pads, and the strip’s specific-gravity pad reads only ionic solutes, so it disagrees with a refractometer when heavy non-ionic solutes (such as radiographic contrast) are present.^[5]

Microscopic Sediment

Casts are the highest-yield microscopic finding because they form in the renal tubule and therefore localize disease to the kidney. Muddy-brown granular casts indicate acute tubular necrosis; red cell casts indicate glomerular bleeding (acute glomerulonephritis); white cell casts indicate pyelonephritis; and broad, waxy casts indicate chronic renal failure. Crystals are identified by shape and urine pH: hexagonal cystine crystals point to cystinuria, and envelope-shaped calcium oxalate crystals are common.^[5]

CSF & Other Body Fluids

In cerebrospinal fluid, bacterial meningitis shows a high WBC count with neutrophil predominance, high protein, and low glucose(bacteria consume it), while viral meningitis shows a lymphocyte-predominant count with normal glucose. Normal adult CSF has 0–5 WBC/µL and a glucose about 60–70% of the plasma value. For serous fluids (pleural, peritoneal), Light’s criteria distinguish a transudate (a filtration imbalance) from an exudate (an inflammatory/malignant process); meeting any one criterion makes it an exudate.^[5]

Chemistry

Clinical Chemistry is 17–22% of the exam.^[1] It spans carbohydrates, lipids, proteins and enzymes, acid-base and electrolytes, endocrinology, therapeutic drug monitoring, and toxicology — with a strong emphasis on interpreting an analyte against a disease state and doing the calculations.

Carbohydrates, Lipids & Proteins

Hemoglobin A1c reflects the average glucose over ~2–3 months; ≥6.5% is diagnostic of diabetes, and an oral glucose tolerance test 2-hour value of ≥200 mg/dL is also diagnostic. For lipids, the Friedewald equation estimates LDL = total cholesterol − HDL − (triglycerides ÷ 5), valid only when triglycerides are below ~400 mg/dL. Apolipoprotein B reflects atherogenic particle number and adds cardiovascular risk information beyond LDL.^[5][6]

Enzymes & Cardiac Markers

Enzyme patterns localize disease. ALT and ASTmark hepatocellular injury (an AST:ALT ratio >2:1 suggests alcoholic liver disease); alkaline phosphatase rises in cholestasis and bone disease; lipase is more pancreas-specific and longer-lived than amylase in pancreatitis. The most cardiac-specific marker is cardiac troponin; with high-sensitivity assays, CK-MB’s main remaining role is estimating infarct size and detecting reinfarction.^[5]

Electrolytes & Acid-Base

The anion gap = Na − (Cl + HCO₃), normally ~8–12 mmol/L. A high gap means a metabolic acidosis from unmeasured acids (lactate, ketoacids, toxins). Reading a blood gas follows a simple logic: the pH tells you acidosis vs alkalosis; if PCO₂ moves opposite the pH it is respiratory, and if HCO₃ moves with the pH it is metabolic.^[5]

Endocrine, TDM & Toxicology

Endocrine testing relies on stimulation/suppression logic and feedback loops — for example, a high parathyroid hormone with a high calcium indicates primary hyperparathyroidism. Therapeutic drug monitoring measures the trough (lowest, pre-dose) level to confirm the drug stays in range and is not toxic; common monitored drugs include gentamicin, digoxin, phenobarbital, lithium, and tacrolimus. Toxicology covers alcohols, heavy metals (lead), acetaminophen, and drugs of abuse.^[1][5]

Hematology

Hematology is 17–22% of the exam.^[1] It covers blood and marrow physiology, the anemias and the leukemias, hemostasis and coagulation, and the morphology and laboratory tests that evaluate them — with constant smear-interpretation and calculation questions.

Red Cells, Indices & Anemias

The red cell indices are calculated from the CBC: MCV (size) = Hct ÷ RBC × 10, MCH = Hgb ÷ RBC × 10, and MCHC= Hgb ÷ Hct × 100. The MCV sorts anemia into microcytic, normocytic, and macrocytic — the single most useful first step. Iron deficiency shows a low ferritin with a high TIBC; a megaloblastic (B12/folate) anemia shows hypersegmented neutrophils.^[5]

White Cells & Leukemias

Auer rods in blasts are diagnostic of acute myeloid leukemia. Chronic myeloid leukemia is defined by the Philadelphia chromosome, t(9;22), producing BCR-ABL1, while acute promyelocytic leukemia carries t(15;17) (PML-RARA).

Reed-Sternberg cells mark Hodgkin lymphoma. The myeloproliferative neoplasms (including polycythemia vera) are most often driven by JAK2 V617F.^[5]

Hemostasis & Coagulation

Coagulation testing maps to the cascade. The PT/INR measures the extrinsic and common pathways and monitors warfarin; the aPTT measures the intrinsic and common pathways and monitors heparin. Hemophilia A is factor VIII deficiency, hemophilia B is factor IX deficiency.

In DIC, the PT and aPTT are prolonged, platelets and fibrinogen fall, and the D-dimer rises. Factor V Leiden is the most common inherited thrombophilia.^[5]

Morphology & Special Tests

Smear morphology is heavily tested. Schistocytes (fragmented helmet cells) with a negative DAT point to a microangiopathic hemolytic anemia (DIC, TTP, HUS).

Teardrop cells suggest myelofibrosis; Howell-Jolly bodies indicate a post-splenectomy state;target cells accompany thalassemia and liver disease; sickle cellsreflect the beta-globin glutamate→valine substitution. The reticulocyte count (residual ribosomal RNA stained by new methylene blue) gauges marrow response.^[5]

Immunology

Immunology is 5–10% of the exam.^[1] It covers immune-system physiology and immunoglobulins, hypersensitivity and autoimmunity, transplantation, and infectious-disease serology — the principles that also underpin the antibody work in blood banking.

Immune System & Immunoglobulins

The innate response (complement, phagocytes, NK cells) is immediate and non-specific; the adaptive response (B and T cells) is specific and remembers. IgM is a pentamer, made first in the primary response and the best complement activator.

IgG is the most abundant, dominates the secondary response, and is the only class that crosses the placenta — which is exactly why IgG (not IgM) alloantibodies cause HDFN. The complement cascade’s central step is cleavage of C3 by a C3 convertase.^[5]

Hypersensitivity & Autoimmunity

The Gell and Coombs hypersensitivity classification is a guaranteed topic: Type I immediate/IgE (anaphylaxis), Type II antibody-mediated cytotoxicity (hemolytic transfusion reaction), Type III immune-complex (SLE, serum sickness), and Type IVdelayed/T-cell (contact dermatitis, the PPD reaction, 48–72 hours). Loss of self-tolerance — often a failure of central tolerance — underlies autoimmunity.^[5]

Serologic Testing

Serology detects autoantibodies and infections. The antinuclear antibody screen (indirect immunofluorescence on HEp-2 cells) is the gold standard for SLE; rheumatoid factor is an autoantibody (usually IgM) against the Fc of the patient’s own IgG. Syphilis testing pairs nontreponemal screens (RPR/VDRL) with treponemal confirmation, and a positive heterophile (Monospot) test supports infectious mononucleosis.^[5]

Microbiology

Microbiology is 17–22% of the exam.^[1] It covers pre-analytic, analytic, and post-analytic procedures across bacteriology, plus mycobacteriology, virology, parasitology, and mycology — with organism identification as the dominant theme.

Specimens, Gram Stain & Setup

Identification starts with the Gram stain: read the reaction (color), morphology (shape), and arrangement. Gram-positive organisms retain crystal violet because of a thick peptidoglycan layer; Gram-negative organisms stain pink.

The acid-fast stain (Ziehl-Neelsen) detects mycolic-acid-rich cell walls and identifies Mycobacterium. Specimen quality and correct media/incubation conditions are pre-analytic essentials.^[5]

Gram-Positive Organisms

Among Gram-positive cocci, the catalase test separates staphylococci (positive) from streptococci/enterococci (negative), and the coagulase test then identifies Staphylococcus aureus (positive). Streptococci are sorted by hemolysis: beta-hemolytic group A = S. pyogenes (bacitracin/PYR positive); alpha-hemolytic, optochin-sensitive, bile-soluble = S. pneumoniae; and bile-esculin positive in chains = Enterococcus.^[5]

Gram-Negative Organisms

Gram-negative rods are sorted by the oxidase test and lactose fermentation. Oxidase-negative lactose fermenters (pink on MacConkey) like E. coli are Enterobacterales; Pseudomonas aeruginosa is an oxidase-positive non-fermenter with blue-green pigment. Proteus swarms and is urease-positive; Salmonellashows black centers (H₂S) on HE agar; and Neisseria gonorrhoeae is an oxidase-positive Gram-negative diplococcus on Thayer-Martin.^[5]

Susceptibility, Myco, Viro & Para

Antimicrobial susceptibility testing reports an isolate as susceptible, intermediate, or resistant. The minimum inhibitory concentration (from broth microdilution) is compared with CLSI (M100) breakpoints; Kirby-Bauer disk diffusion gives a categorical result from zone diameters with a standardized 0.5 McFarland inoculum. Beyond bacteriology, know Mycobacterium (acid-fast), the hepatitis and other viral serologies, the major parasites, and key fungi (e.g. Cryptococcus with a capsule on India ink, Candida germ-tube positive).^[4][5]

Laboratory Operations

Laboratory Operations is 5–10% of the exam.^[1] It is the quality, safety, mathematics, instrumentation, and management framework that makes every result trustworthy — the cross-cutting layer over all six benches.

Quality Control & Westgard Rules

Quality control runs known control materials to confirm a method is performing before patient results are reported. A Levey-Jennings chart plots daily controls against the mean with ±1, ±2, and ±3 SD bands. The Westgard multirules then decide acceptability: a single point beyond ±3 SD violates the 1₃ₛrule (reject and investigate), while a point between ±2 and ±3 SD is a 1₂ₛ warning that prompts checking the other rules rather than auto-rejecting.^[5]

QA, Proficiency Testing & Regulation

Quality assurance monitors the whole testing process across the pre-analytical, analytical, and post-analytical phases. Proficiency testing sends blind samples to many labs and compares results to verify accuracy against peers, and a delta check flags a large unexpected change from a patient’s prior result. CLIA sets the federal minimum standards for all U.S. clinical testing; CAP and The Joint Commission accredit laboratories.^[1]

Lab Math & Instrumentation

Expect laboratory mathematics: dilutions and serial dilutions, concentration and molarity, standard curves, and the diagnostic statistics — sensitivity (true positives detected), specificity (true negatives detected), and predictive values. Distinguish accuracy (closeness to the true value) from precision (reproducibility). Core instrumentation includes spectrophotometry (Beer’s law), electrophoresis, chromatography, mass spectrometry, and flow cytometry.^[1][5]

How to Use This Study Guide

Work through the guide one content area at a time. After each one, check it off in the contents to raise your exam-readiness score, then drill the same content in our free practice questions and flashcards— active recall and interpretation practice are what move knowledge into exam-day performance.

• Weight your time by the percentages. The four 17–22% benches deserve the most study; the three 5–10% areas come after.
• Interpret, don’t just memorize. The MLS rewards correlating a result to a disease state and troubleshooting — that is the bachelor-level edge over the technician exam.
• Master the algorithms. DAT vs IAT, the MCV anemia fork, the Gram-stain ID tree, and acid-base interpretation are reusable across dozens of questions.
• Be fast on the math. Anion gap, osmolality, red cell indices, dilutions, and sensitivity/specificity recur as procedural items.
• Then prove it. When a content area feels easy, confirm it with our practice questions and flashcards.

Common questions MLS candidates search and get asked — each answered briefly and backed by an official source (ASCP BOC, AABB, NIH, CLSI, or CDC). Tap any card to test yourself.

ASCP MLS Glossary

Key medical-laboratory-science terms in one place. Hover any dotted term throughout the guide for its definition; the full list is below.

MLS

Medical Laboratory Scientist — the ASCP Board of Certification credential, written MLS(ASCP), for a baccalaureate-level scientist who performs and interprets complex testing across all areas of the clinical laboratory.

ASCP

American Society for Clinical Pathology — whose Board of Certification (BOC) develops and awards the MLS(ASCP) credential, the leading clinical-laboratory certification in the United States.

BOC

The ASCP Board of Certification — the credentialing arm of the ASCP that issues the MLS and other laboratory credentials.

CAT

Computer Adaptive Testing — the exam selects each next question based on your prior answers; the MLS exam is a 100-question CAT.

blood banking

The laboratory discipline (immunohematology) covering blood groups, antibody detection, compatibility testing, and transfusion practice.

immunohematology

The study of red cell antigens and antibodies and their reactions — the science behind blood banking and transfusion.

ABO system

The most important blood-group system: A, B, AB, and O groups defined by the A and B carbohydrate antigens and the naturally occurring anti-A/anti-B isoagglutinins.

isoagglutinin

A naturally occurring ABO antibody (anti-A or anti-B) directed against the A or B antigen a person lacks.

Rh system

The blood-group system whose D antigen is the most immunogenic non-ABO antigen; Rh-positive means the D antigen is present.

D antigen

The most immunogenic Rh antigen; anti-D in an Rh-negative mother causes the classic severe form of HDFN.

Bombay phenotype

A rare phenotype (hh) lacking the H antigen, so no A, B, or H antigen forms; the person makes potent anti-H and can receive only Bombay (hh) blood.

DAT

Direct antiglobulin test — detects red cells already coated in vivo with antibody or complement, performed on the patient's washed cells with no incubation.

IAT

Indirect antiglobulin test — detects in vitro sensitization by incubating the patient's plasma with reagent red cells; used for the antibody screen, ID, and crossmatch.

AHG

Anti-human globulin (Coombs) reagent — bridges IgG or complement bound to red cells to produce visible agglutination in the DAT and IAT.

crossmatch

Pretransfusion testing that confirms compatibility between donor red cells and recipient plasma; a major crossmatch tests donor cells against recipient plasma.

antibody screen

A pretransfusion test of the patient's plasma against reagent screening cells to detect clinically significant unexpected (non-ABO) antibodies.

HDFN

Hemolytic disease of the fetus and newborn — maternal IgG antibody crosses the placenta and destroys fetal red cells; the classic severe form is anti-D.

RhIG

Rh immune globulin — anti-D given to D-negative mothers to prevent anti-D alloimmunization after exposure to D-positive fetal cells.

dosage effect

Stronger antibody reactivity against red cells with a homozygous (double-dose) antigen than a heterozygous one; classic for Kidd and Duffy antibodies.

DHTR

Delayed hemolytic transfusion reaction — an anamnestic antibody (often Kidd) rises days after transfusion and hemolyzes the transfused cells.

FNHTR

Febrile non-hemolytic transfusion reaction — a temperature rise of at least 1°C with chills during transfusion, without hemolysis.

anion gap

Sodium − (chloride + bicarbonate), normally about 8–12 mmol/L; a high gap signals a metabolic acidosis from unmeasured acids.

troponin

The most cardiac-specific biomarker; cardiac troponin I or T rises after myocardial injury and is the standard for diagnosing myocardial infarction.

HbA1c

Glycated hemoglobin reflecting average blood glucose over ~2–3 months; ≥6.5% meets the diagnostic threshold for diabetes.

Friedewald equation

An estimate of LDL cholesterol = total cholesterol − HDL − (triglycerides ÷ 5), valid when triglycerides are below ~400 mg/dL.

MCV

Mean corpuscular volume — average red cell size; classifies anemia as microcytic (<80 fL), normocytic (80–100 fL), or macrocytic (>100 fL).

ferritin

The body's main iron-storage protein; a low ferritin is the most specific indicator of iron-deficiency anemia.

PT/INR

Prothrombin time / international normalized ratio — measures the extrinsic and common pathways and monitors warfarin.

aPTT

Activated partial thromboplastin time — measures the intrinsic and common pathways and monitors unfractionated heparin.

Auer rods

Needle-shaped cytoplasmic inclusions of fused primary granules seen in myeloblasts; diagnostic of acute myeloid leukemia.

JAK2 V617F

The mutation found in most myeloproliferative neoplasms, including polycythemia vera.

Philadelphia chromosome

The t(9;22) translocation producing the BCR-ABL1 fusion gene; the hallmark of chronic myeloid leukemia.

schistocytes

Fragmented red cells (helmet/triangle shapes) seen in microangiopathic hemolytic anemia such as DIC, TTP, and HUS.

hypersensitivity reaction

An exaggerated immune response classified by Gell and Coombs as type I (IgE/anaphylactic), II (cytotoxic), III (immune-complex), or IV (delayed, T-cell).

IgM

A pentameric immunoglobulin, first made in the primary response and the most efficient complement activator; it cannot cross the placenta.

IgG

The most abundant serum immunoglobulin, dominant in the secondary response and the only class that crosses the placenta.

ANA

Antinuclear antibody — autoantibodies against nuclear components, screened by indirect immunofluorescence on HEp-2 cells; a marker of SLE and other autoimmune disease.

catalase test

Adds hydrogen peroxide to Gram-positive cocci; bubbling (positive) identifies staphylococci, no bubbling (negative) identifies streptococci/enterococci.

coagulase test

Distinguishes Staphylococcus aureus (coagulase-positive, clots plasma) from coagulase-negative staphylococci like S. epidermidis.

oxidase test

Detects cytochrome c oxidase; positive in Pseudomonas and Neisseria, negative in Enterobacterales.

MIC

Minimum inhibitory concentration — the lowest antimicrobial concentration that visibly inhibits growth; compared to CLSI breakpoints to report susceptibility.

acid-fast stain

The Ziehl-Neelsen stain that detects mycolic-acid-rich cell walls; identifies Mycobacterium species such as M. tuberculosis.

quality control

Running known control materials to confirm a test or instrument is performing correctly before patient results are reported.

quality assurance

The broad, ongoing monitoring of the whole testing process across the pre-analytical, analytical, and post-analytical phases.

Levey-Jennings chart

A plot of daily control values against the mean with ±1, ±2, and ±3 SD bands, used to spot trends and shifts.

Westgard rules

Multirule QC criteria (1₂s, 1₃s, 2₂s, R₄s, 4₁s, 10ₓ) that decide whether an analytical run is in or out of control.

delta check

A QC comparison of a patient's current result with a recent prior result; a large unexpected change flags a possible error or mix-up.

proficiency testing

External blind samples sent to the lab to verify its results agree with peer laboratories; a CLIA requirement for many analytes.

accuracy

How close a measured result is to the true value (assessed against reference materials and proficiency testing).

precision

How reproducible repeated measurements are, quantified by the standard deviation and coefficient of variation.

CLIA

The Clinical Laboratory Improvement Amendments — the federal regulations setting minimum quality standards for all U.S. clinical laboratory testing.

ASCP MLS Study Guide FAQ

References

1. 1.ASCP Board of Certification (BOC). “Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi) — Examination Content Guideline & Outline (Revised July 2023).” ASCP. ↑
2. 2.ASCP Board of Certification (BOC). “About the Examination — Computer Adaptive Testing, Scaled Scoring & Eligibility Routes.” ASCP. ↑
3. 3.Association for the Advancement of Blood & Biotherapies (AABB). “Standards for Blood Banks and Transfusion Services (Compatibility, Crossmatch, Transfusion Reactions).” AABB. ↑
4. 4.Clinical and Laboratory Standards Institute (CLSI). “Performance Standards for Antimicrobial Susceptibility Testing (M100) & Laboratory QC Standards.” CLSI. ↑
5. 5.National Institutes of Health / National Library of Medicine. “StatPearls & MedlinePlus (anemia, coagulation, urinalysis, microbiology identification, immunology).” NIH/NLM. ↑
6. 6.Centers for Disease Control and Prevention (CDC). “Diabetes Diagnosis (A1C), Laboratory Quality, and Infectious-Disease Testing Guidance.” CDC. ↑

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