Medical School - ClinicalOsteopathic Medicine

COMLEX vs USMLE: A Comparison for Osteopathic Medical Students

Understand the unique preparation an osteopathic student needs to succeed on COMLEX compared to USMLE, differences between the two exams, and test-taking strategies.

With the recent ACGME and AOA residency position merger, MD and DO students, and their training, may seem more alike than ever. Preclinical years are spent taking similar courses, studying the same or similar materials, and purchasing the same products for board prep. In 2018, approximately 60% of osteopathic students sat for USMLE Step 1 in order to improve their standing on the rank order lists of residency programs and that percentage is certainly even higher today. Given the rising number of osteopathic students who are taking the USMLE examination and the near identical training, one might think that USMLE exams and COMLEX exams would be very similar in question style, content, and topical distribution. However, students will find that the two exams are two different experiences, despite sharing a similar objective. An osteopathic student who plans to take USMLE will need to do additional and unique preparation to succeed on COMLEX. Below are some differences between the two exams and study tips for test takers.

COMLEX is “Vague”

COMLEX questions are vague. We hear this consistently from students, but what does that mean, you are asking. We will do our best to explain it here with an example, but first let’s describe a Step question for comparison. A Step question will often include a long and winding patient history, with some distracting information. Students are forced to pick out the important clinical information embedded within this large paragraph. There is typically objective information, such as vital signs, a CBC, BMP, or imaging included to help students make their way through a long differential to arrive at the most likely diagnosis. The question may simply be asking for the diagnosis – a first order question, or it may force students to use this diagnosis to answer a second or third order question.

On the other hand, COMLEX questions tend to have shorter stems. The history is not as long, and there is less distracting information. On the surface this may make it seem like COMLEX questions are easier. However, this just means that COMLEX questions force students to pick up on vague associations in order to arrive at the “most correct” answer choice (think idiopathic pulmonary hypertension in young women, or thalassemia in a young Greek boy).  The USMLE Step questions are moving away from these associations and are even using them against students to show that these pathologies are not unique to a race, nationality or gender, and that students must rely on their clinical knowledge to arrive at such diagnoses.

Let’s look at an example:

A 29-year-old obese female presents to the emergency department with non-radiating epigastric abdominal pain. She states she was out binge drinking with friends 48 hours earlier and awoke this morning with abdominal pain associated with nausea and vomiting. Food intake does not change the pain. She denies fevers, chills, palpitations, or shortness of breath. Vital signs are normal. Her lipase is 180 (reference range: 10-140). The most likely diagnosis is

  1. appendicitis
  2. cholecystitis
  3. diverticulitis
  4. pancreatitis
  5. pregnancy

This is typical of COMLEX. The differential diagnosis for abdominal pain with nausea and vomiting in a young healthy female is broad, and the question is rather vague. There is no past medical history provided, the description of the abdominal pain is brief, and there is no other lab work or imaging provided to assist us outside of a borderline lipase level. The question seems to be forcing us to rule things out one at a time. Diverticulitis is rare in this patient population, and without a fever, left lower quadrant abdominal pain or a pathologic CT scan, we can rule it out. Appendicitis, while possible, would typically present with a right lower quadrant pain with a white count and a positive imaging test. Cholecystitis is plausible here, but we are not told about right upper quadrant pain, the pain is unrelated to food intake and we have no RUQ ultrasound even though we would really like it. Pancreatitis seems possible with a history of recent binge drinking, and a questionable lipase, but we need 2 of the 3 criteria to diagnose it, and we are missing the classic abdominal pain that radiates to the back, and we do not have any imaging. That leaves us with pregnancy. In a young female with nausea, vomiting, and abdominal pain, with no other proof of pathology, we cannot rule out pregnancy given the information in the stem, making pregnancy the most likely diagnosis. Vague. The takeaway when studying and preparing for the COMLEX exam: do not reach for an answer. It must fit logically. If there is a missing piece to your diagnosis, take a step back and rethink the question.

Length and Timing

Another difference between the two exams that many may not be aware of is length and timing. See the table below for a summary of differences. Step 1 is a 280-question exam divided into 7 blocks of 40 questions each with 1 hour allotted for each block. On the other hand, COMLEX Level 1 is a 352-question exam divided into 8 blocks of 44 questions. However, rather than allotting 1 hour for each block, COMLEX is instead divided into morning and afternoon sessions of 4 hours each, in which students must complete 176 questions (4 blocks of 44 questions) at their own pace. Overall, students taking COMLEX have 8 fewer seconds per question. Also, of note, the USMLE allows 45 minutes of break time to be divided however students would like. If the student skips the tutorial another 15 minutes is available for break time. In contrast, the COMLEX break schedule is far more rigid. Students are given a 10-minute break after block 2, a 40-minute lunch break after block 4, and another 10 minutes after block 6. In COMLEX, students must complete 100 straight questions before being able to take a break, 2.5x the amount students must complete before having the option of a break on Step. All of this is incredibly important when practicing for the exam as students must practice sitting for sets of nearly 100 questions at a time, and must have the stamina for 352 items, a 26% increase in questions.

Level 1 and Level 2 Step 1 Step 2
Number of Items 352* 280 318
Blocks 8 x 44 items 7 x 40 items 8 x 40 items max
Testing session duration 9 hours 8 hours 9 hours
Time per item 82 seconds 90 seconds 90 seconds
Breaks 60 minutes total (2 10-min and 1 40-min for lunch) 45 minutes total – up to 6 separate breaks (60 minutes total if tutorial is skipped) 45 minutes total – up to 6 separate breaks (60 minutes total if tutorial is skipped)

*Level 1 will consist of 352 test items as of May 4, 2021. Prior to this date it has 400 test items.

Study Tip to Help Manage Time:
As you take practice questions, try to form a differential diagnosis immediately, based on limited information. For example, consider a stem that starts, “A 20-year-old male presents with one day of abdominal pain.” Even with this brief sentence, you already have a good deal of information. 20-year-old, making colorectal cancer less likely. Male, meaning inguinal hernias should be considered. One day, indicating an acute pathologic process. You should be able to make a fairly long list of possible diagnoses. With each additional piece of information, change your differential. Now, the young man in the stem has fever. Then, we find the pain is epigastric. Has your differential narrowed? Now you are well-prepared to interpret lab or imaging results, if provided. You will not be surprised when the stem alerts you to a blood alcohol content of 0.3 percent. Your mind has already done the first steps towards making a diagnosis, and you are primed to answer a question about pancreatitis. This kind of item dissection, when performed during practice questions, can help to train you to make the most of limited information. Some students also prefer to read the last sentence of the stem first, to reveal the question being asked, which may influence the differential diagnosis. Also glancing at the answer options, may help narrow the differential. You should practice different strategies to see what works best for you.


The obvious difference between the two exams is the inclusion of osteopathic manipulative medicine, or OMM on COMLEX. Osteopathic principles appear in the form of “pure OMM” items as well as in items primarily involving other disciplines. A pure OMM item is designed to test the student’s understanding of OPP directly. A reliable example is an item that provides structural exam findings at pelvic landmarks along with the results of an anterior compression test. This item will ask for a somatic dysfunction diagnosis and would be considered a pure OMM item. Expect the COMLEX Level 1 and Level 2 exams to have 15% of the total questions of this nature – that is more than 50 questions of pure OMM on each COMLEX exam.

Furthermore, osteopathic physical exam (PE) findings are frequently included in question stems, in an integrated manner. For example, the following is typical of a COMLEX question: “Patient presents with right lower quadrant pain…. on exam, the patient has a tender point at the 11th rib on the right. Vitals are significant for a fever and tachycardia, and labs display a leukocytosis.” Both MD and DO students will likely realize the exam is hinting at appendicitis and will select their answer accordingly. The inclusion of the tender point finding is superfluous since there is enough information to get the answer without it. Nevertheless, recognition of these tender points, and other common osteopathic PE findings may help students get the right answer even faster, an important factor on an exam that is fast paced to begin with. On the other hand, ignoring OMM while studying can be detrimental since a misinterpreted PE finding can throw confusion onto an otherwise clear-cut question and cost valuable time. Being well-versed in OMM is beneficial for pure and integrated OMM items and can have a significant impact on your score.

Study Tip: Whether you plan to use OMM in your practice or not, it is worthwhile to become proficient in OMM for test day. The good news is that the OMM needed to succeed on COMLEX is attainable. High-yield information is well-defined in a bank such as TrueLearn’s COMLEX Level 1 and Level 2 SmartBanks. Common somatic dysfunctions, indications, and contraindications to treatment, and common OMM procedures should all be understood and set to memory. Proficiency in OMM will pay off on test day!

Topic Distribution and Content

Finally, let’s briefly touch on topic distribution and content of the questions themselves. USMLE tends to evenly distribute their questions between the various systems (cardiology, gastroenterology, hematology, etc.). COMLEX on the other hand, is much heavier on the musculoskeletal system, microbiology, and ethics. (COMLEX level 2 also tests USPSTF guidelines for screening and diagnosis.) After all, they have an extra 72 questions to play around with.

MSK: questions focus heavily on dermatomes and nerve roots, frequently asking students which nerve is compressed in various clinical scenarios.

Microbiology: there seems to be more questions overall on COMLEX, and specifically focusing on more esoteric bugs. There is an increased focus on parasitology and mycology, at least far more than on Step.

Ethics: Step questions have a few ethical dilemma-type questions, but COMLEX takes it even further by asking students for landmark court cases and laws that developed from them, like the Tarasoff case, or EMTALA.

USPSTF: COMLEX level 2 loves these guidelines and other primary care questions that develop from it. Students are almost guaranteed to have questions on when to screen for an abdominal aortic aneurysm, whom to screen for lung cancer, and with which diagnostic modality.

These differences in examination content should sway students to focus on board review materials that match their examination.

Key Points for Exam Success

  1. COMLEX questions can be vague. Do not pick an answer that you cannot logically reason out. If it does not exactly fit, it is not right.
  2. COMLEX is a longer exam with a rigid break schedule. Simulating the exam is crucial, and practice tests are needed that can exactly replicate the exam. Sitting and starting at questions for 8 hours is grueling. Practice it.
  3. Do not ignore OMM. It can make all the difference in boosting or hurting your COMLEX score.
  4. COMLEX does not evenly distribute questions. MSK, micro, and ethics are disproportionately favored. Review accordingly.

Taking licensing examinations is inherently stressful, but with the right preparation that stress can become manageable. While you cannot know exactly what is going to be tested on exam day, you may have a pretty good sense of how, that is, the style, length, and scope of exam items. For those taking both COMLEX and USMLE exams, preparation should include both the what – medical knowledge – and the how – the style and peculiarities of each exam. Implement the suggestions above and you will be on your way to licensing exam success!


TrueLearn empowers learners to perform at their absolute highest levels on high-stakes licensure, board certification, and in-training examinations. Since 2007, the company's SmartBanks have helped hundreds of thousands of students and resident physicians to become better learners, thinkers, and test-takers.

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