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NBME Free 120: Everything You Need to Know + Question Explanations

So, it’s your final week of Step 1 studying. Congratulations! Are you wondering what should you do in that final week of studying? One resource I am a big fan of having my students use in the final week of Step 1 studying is the NBME Free 120 questions. But before we get into why it’s extremely helpful in that last week, let’s discuss what it is.

What is the NBME Free 120?

The NBME free 120 is a set of 120 questions given by NBME that you can utilize within their web interface. The Free 120 simulates the exact format of the USMLE Step 1, question style and length, and user interface (i.e how the screen looks, how break time looks, etc).

It is 3 blocks of 40 questions timed exactly like the USMLE Step 1, it gives you the exact same tutorial, and it allows you to check your answers (without explanations) once you’ve finished.

Free 120 Drawbacks

The major drawback of this simulation exam is that it only gives you a percentage correct and not a scaled score. We will talk more about that later. Now that we know what the NBME Free 120 is, let’s talk about how to use it and why it’s helpful.

How to Use the NBME Free 120

1. Use the Free 120 as a test day simulator 4-5 days before your actual test date.

This is a low-stress exam as there is no scaled score, and it mimics breaks, question style and length, and difficulty to a certain extent. It is essentially a dry run of what you will do on test day and has no psychological impact on your prep, as it doesn’t give a three-digit score.

One key reason you should take the Free 120 that close to your exam is that these questions are known to show up verbatim on Step 1. Remember, on the Step 1, the graders (or computers who grades it) don’t care if you got lucky and picked the correct answer. A correct answer is a point, so NBME is essentially giving you 3-5 free points with this Free 120.


2. Utilize the test tutorial in the Free 120 to save valuable break time on Step 1 test day.

This exam mimics the interface you will see on test day. This includes the test-taking tutorial and interactive questions.

Seeing the tutorial before your test date will allow you to skip it on the day of the exam, which will save you 15 minutes of break time. Trust me when I say you will need all your break time, as it is very important to break in between each block of 40 questions.


3. Acclimate to Step 1 interactive questions.

The interactive questions in the Free 120 include those where you listen with your stethoscope for a murmur or listen to breath sounds. Knowing how these will look on the exam day will help lessen your anxiety, as you will not fidget around figuring out how to use these features. Less anxiety is always a good thing on test day.


How is the NBME Free 120 Scored?

The Free 120 does not generate a three-digit score. It does give you a percentage correct, which some people have tried to correlate to a Step 1 score, but there isn’t any real data about how predictive it is.

Anecdotally, I can say that if a student gets a 75% or higher on the NBME Free 120, they pass Step 1. That’s from a small sample size of about 25-30 students/friends. In terms of actual score, again, there is no direct correlation between your percentage on the NBME Free 120 and your step 1 three-digit score.

NBME Free 120 Question Explanations

To help you make the best of your time with the NBME Free 120, here are explanations for 25 questions. These are the first 25 questions in Block 1 of the Free 120:

1. This answer choice refers to aminoglycosides. Penicillin destroys the cell walls of organisms and allows larger drugs like aminoglycosides to enter the cell and execute their bactericidal effects.

2. This answer choice refers to Gilbert syndrome. This patient has intermittent jaundice likely brought on by stressors (such as infection, dehydration, etc) and has an elevated indirect bilirubin because of it. This is due to decreased activity of UDP glucoronyl transferase which
normally will conjugate bilirubin.

3. This table indicates that the response of the muscle increases in the presence of drug x and acetylcholine. This is because acetylcholine works at the nicotinic receptors as well as muscarinic receptors. Nicotinic receptors are located at the neuromuscular junction and when they are stimulated, they will cause muscle contraction.

4. This question is referring to Rhesus (Rh) factor incompatibility. The reason Rho (D) is given during the third trimester is that there is slight mixing of fetal and maternal blood at around 28 weeks. This causes the mom who is Rh- to be exposed to Rh+ blood cells. This will stimulate the mom’s immune system to produce antibodies to Rh+ cells. To prevent this from happening, Rho (D) is given. Rho (D) is Rh factor immunoglobulin. This immunoglobulin will bind to the fetal cells and prevent maternal cells from recognizing them (although full mechanism is still unknown).

5. This patient has Cardiac Tamponade. In cardiac tamponade, obstructive shock occurs due to decreased right-sided and left-sided heart filling. The reason this occurs is because when the right ventricle fills normally, it expands into the free wall and the septum. When there is fluid in the pericardial space, this expansion can only occur in the direction of the septum which causes compression of the left ventricular cavity. This leads to the characteristic findings of pulsus paradoxus, hypotension and JVD. The muffled heart sounds are due to the fluid around the heart acting as an insulator of the heart sounds. The tachycardia is our bodies compensation to the hypotension via activation of sympathetics to increase heart rate and cardiac output.

6. The overall mechanism of action of metformin is to decrease hepatic gluconeogenesis via suppression of gluconeogenic enzymes and increase the bodies efficiency when using glucose.

7. Around 10% of people with HIV are first diagnosed due to an incidental finding of thrombocytopenia. In patients with thrombocytopenia, one physical finding includes petechiae (tiny bruises).

8. This syndrome the patient developed is due to a type III hypersensitivity reaction called the arthus reaction.

9. In patients without a history of substance abuse, morphine in a controlled setting has a low likelihood of leading to a psychological addiction. On top of that, it is the best choice for adequate pain control post operatively.

10. This woman has irritant contact dermatitis. In her case its likely due to her new hair dye. This is a type IV hypersensitivity and is due to delayed activation of T-cells. The CD markers listed are important in Co-stimulation of the T-cells so that they may produce cytokines and further go on to activate other cells.

11. Malonyl CoA is involved in fatty acid synthesis. Your body likes to be in either catabolism or anabolism at one point in time. It doesn’t like to do both simultaneously, so if you are making fatty acids, the release of them through beta oxidation will be shut down.

12. This is an open-labeled clinical trial as all study participants know which drug they will receive and which dose of the drug they will receive. There is no randomization or blinding.

13. This patient has a pancreatic adenocarcinoma and likely developed a clot due to this. This may be due to the excess mucin produced by pancreatic adenocarcinomas as mucin is thrombogenic. If the clots were in superficial veins and located in multiple different areas, this would be considered Trousseau’s Syndrome which is also called migratory thrombophlebitis.

14. A large ovarian tumor that causes virilization in a female is likely producing testosterone. The only answer choice that corresponds to a tumor that produces testosterone is a Sertoli-leydig tumor. Leydig cells in men will produce testosterone normally but can occur in females in conjunction with this malignancy.

15. This patient likely has a superficial soft tissue infection due to an infected cut. The reason he has edema in this case is due to the inflammatory cells releasing cytokines. Certain cytokines have been shown to cause relaxation of the endothelial cell junctions which promotes third spacing of fluid. This causes fluid in the vasculature to enter the interstitium at a rate faster than it can be cleared which leads to edema.

16. This patient has a pinealoma. The pineal gland is adjacent to the pretectal area. The pretectal area is what is responsible for upward gaze. When it is compressed patients have an upwards gaze palsy which is referred to as Parinaud Syndrome.

17. This patient has a renal infarct. This is likely due to his atrial fibrillation as nonuniform contractions in the atria of the heart lead to stasis of blood. This promotes coagulation. These clots then make their way into the left ventricle and then into the aorta and travel to different arteries causing infarcts via occlusion of a vessel.

18. This patient has hot-tub folliculitis due to pseudomonas aeruginosa. Likely acquired as it entered the follicle which is more open in a hot environment.

19. This patient has H. Pylori. This organism is a gram – heliobacter which stains with silver. It causes antral ulcers as the antrum is the portion of the stomach with the least acidity (highest pH). The
organism then further increases the pH of the area it is in by producing urease which breaks down urea into NH3 which can alkalinize the area and promote further bacterial proliferation.

20. The fibular neck (at the lateral aspect of the leg just below the knee) is the location of the common peroneal (fibular) nerve. At this point it branches into a superficial and deep branch. The superficial branch does sensation to the dorsum of the foot (except for first webbed space) as well as motor function in the lateral foot (eversion). The deep branch provides sensation for the first webbed space and does dorsiflexion of the foot.

21. Fluid accumulates in the most dependent space relative to gravity. If one is lying on their back the fluid will accumulate in the paracolic gutters. If one is standing up it will go to the lowest area in the body that can hold fluid. In women this happens to be the Pouch of Douglas which is the space between the uterus and rectum.

22. TNF alpha inhibitors are a mainstay in the treatment of many autoimmune conditions. They are typically not first line treatment though and are only used after failure of a first line treatment (for
example in rheumatoid arthritis you can use methotrexate first and then if the patient doesn’t respond you would then switch them to a TNF alpha inhibitor or add it on).

23. This patient has bullous pemphigoid. It is characterized by tense blisters which do not separate upon rubbing them (negative Nikolsky sign). There are also no oral lesions in this disease. It is due to autoimmune destruction of hemidesmosomes which are located in the basement membrane layer.

24. Farmers tend to use pesticides during their work which contain organophosphates. This leads to acetylcholine excess, as organophosphates work as acetylcholine esterase inhibitors.
Acetylcholine esterase works to breakdown acetylcholine and when it is inhibited you will be unable to breakdown acetylcholine leading to all these symptoms. To reverse it you must give a muscarinic antagonist, such as atropine, to block the effects caused by this excess acetylcholine.

25. This woman is frail and has difficulty swallowing. In patients with oropharyngeal dysphagia (difficulty initiating swallowing) they are at high risk for aspiration. Other patients at risk for aspiration are those with neurological dysfunction (stroke, Alzheimer’s etc), alcoholics, or
seizure patients. Aspiration of oral flora (gram+ and anaerobes) leads to aspiration pneumonia.


We hope this post helped you make sense of the NBME Free 120 and how to use it for Step 1 prep!