Free ASCP MLS Practice Test (Medical Laboratory Scientist)
MLS(ASCP) practice questions written to the ASCP BOC MLS content guideline, with an explanation for every answer.
A potassium of 6.8 mmol/L is reported on a visibly hemolyzed sample from a patient whose previous result was 4.1 mmol/L. What is the best action?
452 original MLS questions · 29 lab calculation questions in their own drill · 31 MLS-only questions on management, education and advanced topics
MLS practice questions by content area
ASCP’s content guidelines give each area a share of the exam. Each area has a guide with free sample questions and a free ten-question drill with an explanation after every answer.
Blood Banking
17–22% of the MLS · 20 questions on our mock
Blood products and storage, donors, ABO, Rh and other blood group systems, antibody screening and identification, crossmatching, HDFN and transfusion reactions.
Urinalysis and Other Body Fluids
5–10% of the MLS · 7 questions on our mock
Physical and reagent strip testing, urine sediment cells, casts and crystals, renal physiology and disease, and CSF, synovial, serous and other body fluids.
Chemistry
17–22% of the MLS · 20 questions on our mock
Glucose, lipids, bilirubin, enzymes, proteins and nitrogen compounds, blood gases and electrolytes, endocrinology, vitamins, therapeutic drugs and toxicology.
Hematology
17–22% of the MLS · 20 questions on our mock
Red cell, white cell and platelet disorders, leukemias, cell counts, indices and morphology, special stains, flow cytometry and hemostasis testing.
Immunology
5–10% of the MLS · 7 questions on our mock
Immune system basics, antibodies and complement, autoimmune and immunodeficiency disease, transplantation, hepatitis, HIV and syphilis serology, and immunoassays.
Microbiology
17–22% of the MLS · 19 questions on our mock
Specimen collection and processing, media, stains, bacterial identification, susceptibility testing and resistance, mycobacteria, viruses, parasites and fungi.
Laboratory Operations
5–10% of the MLS · 7 questions on our mock
Quality control and Westgard rules, regulation and proficiency testing, safety, laboratory math and instrumentation; the MLS adds management and education principles.
Lab Calculations
29 calculation questions from every area
The calculations ASCP lists for both exams: LDL, indirect bilirubin, A/G ratio, transferrin saturation, creatinine clearance, Beer’s law, corrected WBC, hemocytometer counts, red cell indices and absolute counts, plus dilutions, molarity and QC statistics.
Ready for the full exam?
100 four-option questions in 2 hours 30 minutes, drawn in each MLS content area’s share, with a score for every area and an explanation for every answer.
Or start with the free MLS drillThe ASCP MLS exam at a glance
Answer practice questions written to ASCP’s content guidelines (both revised June 9, 2026), read the explanation for every answer, then take a timed 100-question, 2.5-hour practice exam with a score for every content area. The questions use the composite reference ranges ASCP publishes, because the exam does not give them to you.
The American Society for Clinical Pathology Board of Certification (ASCP BOC) runs both exams at Pearson testing centers. Medical laboratory technicians and scientists perform blood bank, chemistry, hematology, immunology, microbiology and urinalysis testing.
- Exam
- Medical Laboratory Scientist, MLS(ASCP), from the American Society for Clinical Pathology Board of Certification (ASCP BOC)
- Format
- 100 multiple-choice questions, each with four options and one best answer. You must answer each question before moving on; you can flag questions and review them once all are answered, if time remains. An onscreen calculator is provided
- Time
- 2 hours 30 minutes
- Content
- Seven areas (content guideline revised June 9, 2026): Blood Banking 17–22%, Urinalysis and Other Body Fluids 5–10%, Chemistry 17–22%, Hematology 17–22%, Immunology 5–10%, Microbiology 17–22%, Laboratory Operations 5–10% (including basic management and education principles)
- Method
- Computer adaptive testing (CAT): the system estimates your ability from your pattern of answers. Unscored field test questions are mixed in and look like the rest
- Passing score
- Scaled scores run from 100 to 999 and the minimum passing score is 400. ASCP says there is no set number or percentage of questions you must answer correctly
- Results
- Preliminary pass or fail on screen at the end; the official score report follows within four business days. A failing report breaks the score down by content area
- Where
- Pearson testing centers, within the eligibility period in your admission notification
- Retakes
- Up to five attempts under one eligibility route, each with a new application and fee. Your new eligibility period starts no earlier than 30 days after the previous exam
- Renewal
- Credential Maintenance Program: 36 points of continuing education every three years
- Fee
- $260 application fee, non-refundable
- Eligibility
- For example, a baccalaureate degree plus a NAACLS-accredited MLS program completed in the last 5 years; other routes combine the degree and required science coursework with MLT(ASCP) certification and clinical experience, with clinical experience, or with a US military course
Where the exam fits in earning the credential
- Check which eligibility route you meet on ASCP’s MLS credential page; most candidates qualify through an accredited program completed within the last 5 years.
- Apply online with your documentation, transcripts and the application fee ($260). The category and route cannot be changed after you submit.
- Once you are eligible, schedule at a Pearson testing center within the eligibility period on your admission notification.
- Take the exam: you see a preliminary pass or fail on screen, and your official score report follows within four business days.
- Keep the credential through the Credential Maintenance Program: 36 points of continuing education every three years.
Studying for another lab or healthcare exam too? Our phlebotomy practice test covers the NHA CPT exam.
How to use this ASCP exam prep
- Take the free MLS mixed drill to see where you stand across all seven areas.
- Drill the big four first: blood banking, chemistry, hematology and microbiology make up 79 of the 100 questions on our MLS mock.
- Take the calculations drill until the formulas ASCP lists are automatic.
- Learn ASCP’s published reference ranges; the exam does not give them.
- Take the full 100-question practice exam under the 2.5-hour clock, drill your two lowest areas and take it again. Each new sitting draws questions you have not seen first.
Common questions
How many questions are on the ASCP MLT and MLS exams?
Both are 100 multiple-choice questions in 2 hours 30 minutes, each with four options and one best answer. (ASCP’s MLT exam for California state licensure only is 80 questions in 2 hours.) Unscored field test questions are mixed in, and you cannot tell them apart from scored ones.
What score do you need to pass the ASCP exam?
A scaled score of 400 on ASCP’s 100–999 scale. Because the exam is computer adaptive, the score comes from your pattern of answers and the difficulty of the questions, and ASCP says there is no set number or percentage of questions you must answer correctly. Percentages quoted elsewhere for passing do not come from ASCP.
What is the difference between the MLT and MLS exams?
They cover the same seven content areas with different weights. The MLT (technician, usually an associate-degree route) puts more weight on chemistry and hematology (20–25% each); the MLS (scientist, usually a bachelor’s-degree route) weights blood banking, chemistry, hematology and microbiology at 17–22% each and adds management and education principles, chromatography and more advanced hemostasis and microbiology topics.
How much does the ASCP MLT or MLS exam cost?
The application fee is $235 for the MLT(ASCP) and $260 for the MLS(ASCP). It is non-refundable, and each new application after a failed attempt carries the fee again.
How many times can you retake the ASCP exam?
You may take an exam five times under one eligibility route if you still meet its requirements; after five unsuccessful attempts you must qualify under a different route. Each attempt needs a new application and fee, and the new eligibility period starts no earlier than 30 days after your previous exam.
Are reference ranges given during the exam?
ASCP publishes composite reference ranges in each content guideline and says they will not be provided during the exam; other ranges are given when needed. Results appear in both conventional and SI units. The questions here use ASCP’s published ranges.
Does ASCP sell an official practice exam?
Yes. ASCP sells an MLT and MLS Interactive Practice Examination and a BOC Study Guide for MLS and MLT exams. The questions on this site are original practice written to ASCP’s content guidelines; they are not ASCP questions.
Is this mock exam adaptive like the real one?
No. The mock is a fixed set of 100 four-option questions in 2 hours 30 minutes, drawn in each content area’s share of the exam, and it works like the real exam otherwise: you answer each question before moving on and can flag questions to review once all are answered. The result shows your percentage correct and a score for every area, not a scaled score, because ASCP’s scaled scores come from its adaptive model.
Ready for test day?
100 four-option questions in 2 hours 30 minutes, drawn in each MLS content area’s share, with a score for every area and an explanation for every answer.
Or start with the free MLS drillSources
- ASCP BOC: MLT and MLS Examination Content Guidelines (revised June 9, 2026)
- ASCP BOC: About the Examination (format, CAT, scoring, field test questions, calculator)
- ASCP BOC: Medical Laboratory Technician, MLT(ASCP): eligibility routes and $235 fee
- ASCP BOC: Medical Laboratory Scientist, MLS(ASCP): eligibility routes and $260 fee
- ASCP BOC: Examination Results
- ASCP BOC: After the Examination (re-applying, five attempts per route, 30-day wait)
- ASCP BOC: Schedule or Reschedule Your Examination (Pearson testing centers)
- ASCP BOC: MLS and MLT Credential Maintenance Program requirements (36 points, three years)
Original practice questions for exam preparation, written to the ASCP BOC MLT and MLS Examination Content Guidelines (revised June 9, 2026); they are not ASCP exam questions. Independent practice, not affiliated with or endorsed by the American Society for Clinical Pathology (ASCP), the ASCP Board of Certification or Pearson VUE. MLT(ASCP) and MLS(ASCP) are ASCP BOC credentials. Follow your laboratory’s procedures and manufacturers’ instructions in practice.