ASCP MLS Exam Content: Topics and Study Guide

ASCP MLS exam content breakdown

The ASCP BOC guideline revised June 9, 2026 assigns a range of the exam to each area. The ranges apply to the certification exam.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

The official guideline describes a 100-question, multiple-choice exam with one best answer per question. Candidates have 2 hours and 30 minutes. The exam uses computer adaptive testing. Questions can ask about laboratory principles, calculations, interpretation, procedures and quality practices.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

Blood banking

Review ABO and Rh typing alongside other blood group systems, antigen-antibody reactions and the causes of unexpected serologic results. Connect antibody screening and identification with crossmatching and selection of compatible blood. The guideline also includes blood donation, component processing and storage, hemolytic disease of the fetus and newborn, and the laboratory investigation of transfusion reactions.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

For ABO grouping, follow both sides of the test. Forward grouping tests the patient's red cells with anti-A and anti-B reagents. Reverse grouping tests the patient's serum or plasma with known A and B red cells. Compare the results and investigate a discrepancy under the laboratory's procedure before assigning the group.^{22 Health Resources and Services Administration. Guidance for addressing blood type determination.}

Start with pretransfusion testing, Rh and other blood group systems, and transfusion reactions. For hands-on practice, use the Blood bank to investigate an antibody screen and select compatible units.

Chemistry

Review the principles behind common chemistry measurements and connect results with specimen quality and analytical interferences. Study glucose and lipid testing, renal markers, proteins and enzymes, electrolytes, blood gases and acid-base balance. The outline also covers endocrine testing, vitamins, therapeutic drug monitoring and toxicology.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

For example, red cell hemolysis can release potassium into serum or plasma and raise the measured result. Review the hemolysis index when available and follow the laboratory's procedure for an affected specimen. The effect and response depend on the method and the laboratory's limits.^{33 Yin T, et al. The impact of hemolysis-index thresholds on plasma and serum… 2022.}

Use the lessons on glucose testing, sodium and potassium, blood gases, and therapeutic drug monitoring. At the Chemistry station, review results and investigate specimen or method problems.

Hematology

Study blood cell production, counts, morphology and disorders. Practice connecting complete blood count results and red cell indices with blood film findings. Review benign and malignant leukocyte disorders, platelet abnormalities, and sources of inaccurate cell counts. Hemostasis includes coagulation and fibrinolysis, bleeding and clotting disorders, and tests such as the prothrombin time and activated partial thromboplastin time.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

An absolute neutrophil count combines the WBC with the neutrophil fraction of the differential. For a practice calculation, a WBC of 8,000/µL and a total neutrophil fraction of 60% give 4,800 neutrophils/µL: 8,000 × 0.60. Use results from the same specimen, and include separately reported bands when the laboratory's procedure includes them in the count.^{44 Hijiya N, et al. Utility of automated counting to determine absolute neutrophil… 2004.}

Begin with differentials and blood film morphology, anemia evaluation, and hemostasis testing. At the Microscope, count a differential and review morphology.

Microbiology

Follow the specimen through collection, transport, processing, organism identification and reporting. Review the use of microscopy, culture, biochemical methods and molecular methods in the investigation of bacteria. The guideline also covers mycobacteria, fungi, parasites and viruses. Study antimicrobial susceptibility testing alongside the workup and reporting of isolates.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

In blood cultures, collection quality affects the result. Skin organisms introduced during collection can produce a false-positive culture, and inadequate blood volume can reduce detection. Consider the organism and the number of positive sets when reviewing possible contamination, following the laboratory's procedure.^{5,65 Centers for Disease Control and Prevention. Prevent adult blood culture contamination. 2026.6 Centers for Disease Control and Prevention. Primary measure. 2024.}

Start with specimen collection and processing, blood cultures and gram-positive isolates, and antimicrobial susceptibility testing. The microbiology library also has lessons on mycobacteria, mycology, parasitology and virology.

Immunology

Review the immune response, immunoglobulins, complement and antigen-antibody interactions. Study the principles of serologic procedures and how to interpret their results. The guideline includes immune system disorders, transplantation and infectious disease serology.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

For infectious disease serology, identify what each test detects and how it fits into the testing sequence. In syphilis testing, nontreponemal tests detect antibodies to lipoidal antigens. Treponemal tests detect antibodies to antigens from Treponema pallidum. A laboratory can use either type as the first test and follows the appropriate sequence for additional testing.^{77 Papp JR, et al. CDC laboratory recommendations for syphilis testing, United… 2024.}

Read immune system physiology, antigen-antibody interactions, and serologic procedures. The immunology library includes infectious disease testing and immune disorders.

Laboratory operations

Study quality assessment and troubleshooting across the testing process, from specimen receipt through reporting. Review laboratory safety, dilution and concentration calculations, diagnostic performance measures, and the principles of manual and automated instruments. The outline also includes management and education.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

A Levey-Jennings chart shows control results across runs against a mean and standard deviation limits. Practice recognizing an isolated result, a shift and a trend, then apply the laboratory's control rules. Control results must meet the applicable acceptance criteria before patient results are reported.^{8,98 National Center for Health Statistics. 2021 Laboratory Procedures Manual. 2022.9 Standard: control procedures, et al. Accessed October 29, 2026.}

Practice with quality control and method evaluation, laboratory mathematics, and laboratory safety. At the QC workstation, investigate control results before reporting patient results.

Urinalysis and other body fluids

Review urine appearance, reagent strip chemistry and microscopy together. Study cells, casts, crystals, microorganisms and artifacts, as well as renal physiology and related laboratory patterns. The guideline includes physical, chemical and microscopic examination of other fluids, including cerebrospinal, synovial and serous fluids.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

When reviewing urine microscopy, learn where findings come from as well as how they look. Casts form in kidney tubules, and red cell casts indicate bleeding into the kidney. Review the appearance of each cast and report findings according to the laboratory's procedure.^{1010 Centers for Disease Control and Prevention. Provider-Performed Microscopy Procedures. 2016.}

Use the lessons on urine reagent strip testing, urine microscopy, and body fluid cell counts.

ASCP MLS exam calculations and reference ranges

ASCP lists calculations that examinees are expected to know, including red cell indices, absolute cell counts, manual cell counts, creatinine clearance and transferrin saturation. Its guideline also provides composite reference ranges for exam preparation. ASCP says those composite ranges are not provided during the exam and that other ranges are supplied when needed.^{11 American Society for Clinical Pathology… Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi)… 2026.}

Practice red cell and absolute count calculations and manual cell counting calculations. The ASCP BOC examination reference ranges lesson brings the published tables together for review.

Plan your review

The examples above are a starting point. Read the full ASCP BOC MLS content guideline to check the complete scope, calculations and examination reference ranges. Check the ASCP content guidelines and reading lists page for later revisions.

Choose an area in LatticeMLS exam practice, then revisit lessons for subjects you missed. The MLS exam study guide can help you build a study plan and schedule review. For a study order built from a score report, see the ASCP MLS exam retake plan.

LatticeMLS is an independent practice tool and is not affiliated with or endorsed by ASCP BOC. Its practice questions and exam blueprint are its own.