The USMLE Step 1 exam tests your grasp of basic science concepts and their clinical applications. To help you prepare, we’ve curated 10 sample questions covering anatomy, physiology, pharmacology, pathology, biochemistry, microbiology, immunology, behavioral science, genetics, and biostatistics. Each question includes a detailed solution that walks through the reasoning — not just the correct answer.
Use these to gauge your current level and identify weak spots. Ready to test yourself under real conditions?
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Anatomy
Question 1: A 45-year-old man presents with foot drop after a hip replacement. Which nerve is most likely injured?
Options:
- A) Femoral
- B) Obturator
- C) Sciatic
- D) Common fibular (peroneal)
- E) Tibial
Solution: The common fibular nerve (option D) wraps around the fibular neck and is vulnerable during hip surgery or prolonged positioning. Foot drop results from loss of dorsiflexion and eversion. The sciatic nerve (C) gives rise to the common fibular and tibial nerves, but the specific deficit here points to the common fibular branch.
Physiology
Question 2: A 60-year-old with chronic hypertension has a blood pressure of 160/100 mm Hg. Which of the following best describes the change in his left ventricular wall stress?
Options:
- A) Increased due to increased afterload
- B) Decreased due to decreased preload
- C) Increased due to increased preload
- D) Decreased due to increased contractility
- E) No change
Solution: Laplace’s law states wall stress = (pressure × radius) / (2 × wall thickness). Chronic hypertension increases afterload, leading to concentric hypertrophy. Initially, wall stress is increased (option A) due to higher pressure. Over time, hypertrophy reduces wall stress, but the acute change is increased stress.
Pharmacology
Question 3: A patient on warfarin develops a hematoma. Which agent should be administered to reverse anticoagulation?
Options:
- A) Vitamin K
- B) Protamine sulfate
- C) Fresh frozen plasma (FFP)
- D) Desmopressin
- E) Tranexamic acid
Solution: Warfarin inhibits vitamin K–dependent clotting factors (II, VII, IX, X). For urgent reversal, FFP (option C) provides active clotting factors. Vitamin K (A) takes hours to work. Protamine reverses heparin, not warfarin.
Pathology
Question 4: A 55-year-old smoker has a lung mass. Biopsy shows nests of small, blue cells with hyperchromatic nuclei and scant cytoplasm. What is the most likely diagnosis?
Options:
- A) Adenocarcinoma
- B) Squamous cell carcinoma
- C) Small cell carcinoma
- D) Large cell carcinoma
- E) Carcinoid tumor
Solution: Small cell carcinoma (option C) is strongly associated with smoking and presents as small, blue cells with high nuclear-to-cytoplasmic ratio. It often metastasizes early and is treated with chemotherapy, not surgery.
Biochemistry
Question 5: A newborn presents with vomiting, lethargy, and metabolic acidosis. Urine organic acids show elevated methylmalonic acid. Which vitamin is deficient?
Options:
- A) Thiamine (B1)
- B) Riboflavin (B2)
- C) Niacin (B3)
- D) Cobalamin (B12)
- E) Pyridoxine (B6)
Solution: Methylmalonic acidemia results from deficiency of methylmalonyl-CoA mutase, which requires cobalamin (B12) as a cofactor (option D). This leads to accumulation of methylmalonic acid. Treatment includes B12 supplementation.
Microbiology
Question 6: A 30-year-old immunocompromised patient develops pneumonia. Sputum culture on charcoal yeast extract agar shows growth. Which organism is most likely?
Options:
- A) Streptococcus pneumoniae
- B) Haemophilus influenzae
- C) Legionella pneumophila
- D) Mycoplasma pneumoniae
- E) Chlamydia psittaci
Solution: Legionella pneumophila (option C) requires charcoal yeast extract agar with iron and cysteine. It causes atypical pneumonia, especially in immunocompromised hosts. Treatment includes macrolides or fluoroquinolones.
Immunology
Question 7: A child with recurrent sinopulmonary infections has absent B cells but normal T-cell function. Which immunodeficiency is most likely?
Options:
- A) Severe combined immunodeficiency (SCID)
- B) X-linked agammaglobulinemia
- C) Common variable immunodeficiency
- D) Hyper-IgM syndrome
- E) DiGeorge syndrome
Solution: X-linked agammaglobulinemia (option B) is characterized by a block in B-cell maturation, leading to absent B cells and low immunoglobulins. T-cell function is normal. It presents after 6 months of age when maternal IgG wanes.
Behavioral Science
Question 8: A 70-year-old woman with advanced dementia is admitted with pneumonia. The family requests no life-sustaining measures. Which ethical principle is most directly supported?
Options:
- A) Beneficence
- B) Nonmaleficence
- C) Autonomy
- D) Justice
- E) Veracity
Solution: Autonomy (option C) respects the patient’s right to make decisions about her care. Here, the family is acting on the patient’s previously expressed wishes. The principle of autonomy overrides beneficence when the patient refuses treatment.
Genetics
Question 9: A couple has a child with cystic fibrosis. Both parents are carriers. What is the probability that their next child will be a carrier?
Options:
- A) 25%
- B) 50%
- C) 75%
- D) 100%
- E) 0%
Solution: Cystic fibrosis is autosomal recessive. Two carriers (Aa × Aa) have a 25% chance of an affected child (aa), 50% chance of a carrier (Aa), and 25% chance of unaffected (AA). So probability of a carrier is 50% (option B).
Biostatistics
Question 10: A new test for a disease has 90% sensitivity and 80% specificity. The disease prevalence is 10%. What is the positive predictive value (PPV)?
Options:
- A) 33%
- B) 50%
- C) 67%
- D) 90%
- E) 80%
Solution: Use a 2×2 table. Assume 1000 people: 100 have disease, 900 do not. True positives = 90% of 100 = 90. False positives = 20% of 900 = 180. PPV = TP / (TP + FP) = 90 / (90 + 180) = 90/270 = 33.3% (option A).
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