MLS
ASCP Board of Certification Medical Laboratory Scientist (MLS) Examination
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Cheat sheet
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ExploreKey terms
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ExploreStudy plan
Give each week a clear focus.
ExploreCommon mistakes
Understand the traps and how to avoid them.
ExploreCase studies
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ExploreExam-day guide
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ExploreAbout this exam
The Medical Laboratory Scientist (MLS) credential is awarded by the ASCP Board of Certification (BOC), the certification body associated with the American Society for Clinical Pathology. It is the entry-level professional credential for laboratory professionals who perform and interpret clinical testing across the full laboratory - generalist scientists as well as those working in hospital, reference, public health, and physician-office laboratories. Candidates are typically students completing or graduating from an accredited MLS/medical technology program, though internationally trained and experienced technologists also sit for it.
The exam is multiple choice and samples the whole curriculum rather than a single specialty, so preparation has to be broad. Content areas include blood bank/immunohematology, clinical chemistry, hematology and hemostasis, microbiology, immunology and serology, urinalysis and body fluids, molecular diagnostics, and laboratory operations and management. Expect calculation items in chemistry and hematology, antibody-identification and crossmatch logic in blood bank, organism identification and antimicrobial reasoning in microbiology, and quality-control, safety, and regulatory items in operations.
ASCP publishes its own BOC Initial Certification Preparation resources, the MLS Online Review, LabQ case-based content, and review books, and many candidates pair those with a structured content review and timed practice. Confirm current exam content specifications, appointment logistics, and scoring details directly with the ASCP BOC before scheduling, since those details are set by the certifying body and change over time.
What you'll study
About MLS preparation
What is the format of the MLS exam?
It is a computer-delivered, multiple-choice examination covering the full clinical laboratory curriculum rather than one specialty. Confirm the current item format, number of options, and any calculator or reference tools on the ASCP Board of Certification site before test day, since delivery details are set by the certifying body.
How many questions are on the exam and how long do I have?
Those figures are published by the ASCP Board of Certification and are not fixed in general references, so check the current candidate handbook rather than relying on numbers from older study guides or peers who tested years ago. Item counts and seat times are periodically revised.
How difficult is it, and what score do I need to pass?
It is a broad, generalist exam, so difficulty comes from breadth more than from trick questions. Passing standards are set by the certifying body and are not a simple percentage published for candidates to self-score against. Treat any specific pass mark or percentage you hear secondhand as unreliable and verify it with the BOC.
What happens if I do not pass - can I retake it?
Retake eligibility, waiting periods, and any additional fees are governed by ASCP Board of Certification policy and are revised periodically. Read the current candidate handbook before you sit, because the rules that applied to a colleague's attempt may already have changed. Do not budget or schedule around an assumed retake window.
What does the exam cost and how long is the credential valid?
Fees and credential duration are set by the certifying body and are not something to estimate. ASCP does maintain a Credential Maintenance Program (CMP) for laboratory professionals, so plan for ongoing maintenance rather than a one-time, permanent certificate. Verify current fees, validity terms, and CMP requirements directly with ASCP.
In what order should I study the content areas?
Take a diagnostic practice test first and rank the eight content areas by your weakest scores, then study in that order while keeping a short daily rotation through your strongest areas so they do not decay. Spend the most time where low confidence overlaps with heavy exam representation.
Which ASCP preparation resources actually exist?
ASCP offers a BOC Initial Certification Preparation section, an MLS Online Review course, LabQ case-based education, and review books through its store, alongside its journals and ASCPedia resource. Many candidates combine one structured review with a question-based resource; pick based on whether you need content rebuilding or retrieval practice.
What are the most common reasons candidates fall short?
Usually breadth, not depth: over-studying one favorite rotation, skipping urinalysis, body fluids, molecular, and management content, weak calculation and unit-conversion fluency, and slow reading on long clinical vignettes. Practicing under timed conditions exposes the pacing problem early enough to fix it.
How far in advance should I schedule the exam?
Schedule once practice scores are consistently where you want them, not on a fixed calendar date chosen before you started studying. Application processing, eligibility windows, and site availability add lead time, so start the application early and keep your test date movable until your practice results justify it.