The Medical Laboratory Scientist (MLS) certification examination covers seven areas of laboratory practice. Use this guide to explore the subjects, find related lessons and practice, and make a study plan you can adjust.
For a closer look at each subject, see ASCP MLS exam content and topics.
Start with the examination outline
The American Society for Clinical Pathology Board of Certification (ASCP BOC) describes the MLS examination as 100 multiple-choice questions in 2 hours and 30 minutes. It uses computer adaptive testing. Questions can ask you to apply knowledge, calculate or interpret results, and follow laboratory techniques or quality procedures. The ASCP BOC guideline revised June 9, 2026 lists the subjects and the share of the examination assigned to each area.1
Scroll sideways to see all columns
| ASCP BOC content area | Share of the examination |
|---|---|
| Blood Banking | 17–22% |
| Chemistry | 17–22% |
| Hematology | 17–22% |
| Microbiology | 17–22% |
| Immunology | 5–10% |
| Laboratory Operations | 5–10% |
| Urinalysis and Other Body Fluids | 5–10% |
These percentages describe the ASCP BOC examination. LatticeMLS exam practice uses its own questions and blueprint, described below.
Open the ASCP BOC MLS content guideline for the detailed outline, calculations and reference ranges. Use it to make a list of subjects you know well and subjects you want to revisit. As your examination approaches, check for a newer MLS guideline through the ASCP BOC content guidelines page.
What the examination covers
The sections below introduce the seven areas in the ASCP BOC guideline. The linked lessons and activities offer places to start. Use the full guideline to check the breadth of each area.1 You can also choose an area in exam practice.
Blood banking
Study blood collection and components, blood group systems, and the immune reactions behind blood bank testing. The guideline also covers compatibility testing, hemolytic disease of the fetus and newborn, and investigation of transfusion reactions.1
Start with the pretransfusion testing lesson and the transfusion reactions lesson. At the Blood bank, work up an antibody screen and select compatible units.
Chemistry
Review how chemistry tests measure substances such as glucose, electrolytes, enzymes and hormones. The guideline includes acid-base balance, therapeutic drug monitoring, toxicology, specimen problems and interpretation of results.1
Read the sodium and potassium lesson and the blood gas lesson. At the Chemistry station, review a metabolic panel and investigate specimen and method problems.
Hematology
Study blood cell production and disorders, cell counts and morphology, and the methods used to examine them. Hemostasis includes platelet and coagulation physiology, disorders and laboratory testing.1
Use the blood film and differential lesson and the hemostasis lesson. At the Microscope, identify cells, count a differential and review morphology.
Microbiology
Review how specimens are collected and processed, how microorganisms are detected and identified, and how results are reported. The guideline covers bacteria, mycobacteria, fungi, parasites and viruses, along with antimicrobial susceptibility testing.1
Begin with the specimen collection and processing lesson and the antimicrobial susceptibility lesson.
Immunology
Study immune system function and disorders, antigen-antibody reactions, transplantation and testing for infectious diseases. The guideline includes the principles and interpretation of serologic methods.1
Read the antigen-antibody interactions lesson and the serologic procedures lesson.
Laboratory operations
Study quality assessment, troubleshooting and safety across the testing process. The guideline also includes laboratory calculations, instruments and methods, management, and education.1
Read the quality control lesson and the laboratory mathematics lesson. At the QC workstation, investigate control results before reporting patient results.
Urinalysis and other body fluids
Review physical, chemical and microscopic examination of urine, along with renal physiology and associated laboratory patterns. The guideline also covers the examination of other body fluids, including cerebrospinal and synovial fluid.1
Start with the urine microscopy lesson and the body fluid cell counts lesson.
Find a starting point
Choose an exam date if you have one, then decide how much time you can realistically study each day. In study plan setup, choose the MLS exam goal and enter your date and available time. You can leave the date open and change your choices later.
The optional diagnostic asks 20 mixed exam-style questions and moves areas with missed questions toward the front of your plan. It needs a free account. A small set gives you a starting signal, so use your coursework, experience and later practice results as well. If you are signed out, you can first try the 10-question sample in exam practice without an account.
Choose 1 or 2 areas to begin. Keep every examination area in your rotation, including the smaller ones. In My plan, you can change the order as your needs change.
Turn a lesson into practice
Pick a focused subject from the lesson library or continue a guided step. Read for the principle, the method and the laboratory decision. Then close the text and explain the idea in your own words, sketch a process from memory or complete the lesson's self-check. Reopen the lesson to check your answer and correct what you missed.
For example, after the quality control lesson, describe the checks you would make when a control result needs investigation. Read the relevant section again and practice a related question. For calculations, write the setup and units before checking the result.
Recalling information from memory is called retrieval practice. A review of studies in health professions education found benefits from retrieval practice and study spread over time in many of the included experiments. The studies used different methods and assessments, so they do not establish a result for any individual student or this examination.2
Make room for review
Return to a subject on later days. Try to recall it before opening the lesson, then check your explanation. A missed answer gives you a specific passage or calculation to revisit.
With a free account, daily review brings questions and study cards back over time. Questions you miss return sooner. For questions that ask for confidence, choose Sure, Think so or Guessing before checking your answer. Use the choice that reflects how you felt when answering. You can choose a department or focus on items you have missed.
Use exam questions to guide the next session
In exam practice, a free account opens practice sets in one area or across all areas. Choose 10, 25 or 50 questions when available. You can see feedback after each question or at the end, and turn the timer on or off. Free ASCP MLS Practice Questions With Explanations shows what makes a practice question useful and gives 2 example questions.
After a set, review the explanation for each miss and for answers you guessed correctly. Note the subject and the reason for the miss, such as an unfamiliar principle, a calculation setup or a detail you overlooked. Open the linked lesson or area from the results, study the relevant passage, and return to similar material on another day. Results show your performance by area. A few questions in an area provide limited evidence, so look for a pattern across several sets.
Use a full exam for pacing
LatticeMLS is a practice tool with its own questions and blueprint. The site is not affiliated with or endorsed by ASCP BOC.
The timed mock and adaptive exam each have 100 questions. With the timer on, you have 150 minutes. Both use LatticeMLS's own blueprint: 20 questions each in Blood Banking, Chemistry, Hematology and Microbiology, plus 20 shared among Immunology, Laboratory Operations, and Urinalysis and Other Body Fluids. The timed mock uses a fixed set. The adaptive exam chooses questions as you answer. A free account is needed for both.
A completed full exam gives a beta readiness band based on LatticeMLS questions and its simulated standard. The band has not been validated against certification outcomes and does not predict your examination result. Use the results to review pacing, identify missed subjects and select lessons for your next sessions. The exam practice page links to a full explanation of the simulator.
Adjust your plan
At the end of each week, look at the work you completed and the subjects that continued to cause difficulty. Move a weak area earlier in My plan, choose a related lesson and add another practice set. Keep reviewing other areas as you go.
A practical session might include a few daily review items, one lesson or guided step, and a short set of questions. On another day, return to the missed material and try a mixed set. If the schedule is too demanding, reduce the daily workload and revise it around the time you have.
If you are preparing to sit the examination again, the ASCP MLS exam retake plan shows how to set your study order from your score report.
References
- American Society for Clinical Pathology Board of Certification. Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi) Examination Content Guideline. Revised June 9, 2026. Accessed October 29, 2026. ASCP BOC MLS content guideline. Back to text
- Trumble E, Lodge J, Mandrusiak A, Forbes R. Systematic review of distributed practice and retrieval practice in health professions education. Adv Health Sci Educ Theory Pract. 2024;29(2):689–714. doi:10.1007/s10459-023-10274-3 Back to text