USMLE STEP 1 QUESTIONS AND CORRECT ANSWERS (VERIFIED ANSWERS) PLUS RATIONALES 2026 Q&A |
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Core Domains
General Principles (Biochemistry, Immunology, Genetics, Pharmacology)
Organ Systems (Cardiovascular, Respiratory, Renal, GI, Endocrine, Reproductive, Musculoskeletal, Neurology,
Psychiatry)
Hematology & Oncology
Microbiology & Infectious Diseases
Pathology & Pathophysiology
Behavioral Health & Social Sciences
Ethics, Legal Principles, & Patient Safety
Biostatistics & Epidemiology
Anatomy & Embryology
Physiology
Introduction
*This examination is designed to evaluate foundational medical knowledge required for USMLE Step 1. It
assesses your ability to integrate basic science principles with clinical presentations, diagnostic reasoning, and
patient management. Questions are formatted as single-best-answer multiple-choice items, often rooted in
clinical vignettes, to test real-world application and decision-making under time constraints. Emphasis is placed
on pathophysiologic mechanisms, pharmacologic interventions, ethical dilemmas, and evidence-based practice.
,Each question includes a verified correct answer and a concise rationale. Prepare to apply knowledge, not just
recall facts.*
SECTION ONE: QUESTIONS 1–100
Question 1
A 45-year-old man with hypertension presents with acute chest pain radiating to the jaw. ECG shows ST-
segment elevation in leads V2–V4. Which coronary artery is most likely occluded?
A. Right coronary artery
B. Left circumflex artery
C. Left anterior descending artery
D. Posterior descending artery
🟢C
🔴 RATIONALE: ST elevation in V2–V4 indicates an anterior wall myocardial infarction, most often caused by
occlusion of the left anterior descending artery.
Question 2
A 2-year-old child presents with failure to thrive, hepatosplenomegaly, and progressive neurodegeneration. A
lysosomal enzyme assay shows deficient beta-hexosaminidase A. Which substrate accumulates?
,A. Globotriaosylceramide
B. Sphingomyelin
C. GM2 ganglioside
D. Glucocerebroside
🟢C
🔴 RATIONALE: Beta-hexosaminidase A deficiency causes Tay–Sachs disease, leading to GM2 ganglioside
accumulation in neurons.
Question 3
A 68-year-old woman on warfarin for atrial fibrillation presents with acute onset of severe left lower extremity
pain, pallor, and pulselessness. Which laboratory finding is expected?
A. Elevated D-dimer
B. Prolonged PT and INR
C. Thrombocytopenia
D. Elevated factor VIII
🟢B
🔴 RATIONALE: The patient is already on warfarin (therapeutic INR), but acute arterial occlusion requires urgent
anticoagulation. The expected lab finding is prolonged PT/INR due to warfarin effect, not the cause of
embolism. Embolic source is likely cardiac.
Question 4
, A medical student accidentally sticks herself with a needle used on an HIV-positive patient. Which post-
exposure prophylaxis regimen is recommended within 72 hours?
A. Tenofovir disoproxil fumarate alone
B. Zidovudine monotherapy
C. Tenofovir disoproxil fumarate + emtricitabine plus raltegravir
D. Ritonavir-boosted lopinavir alone
🟢C
🔴 RATIONALE: Current CDC guidelines recommend a three-drug regimen (two NRTIs plus an integrase
inhibitor) for high-risk HIV exposures.
Question 5
A 55-year-old man with chronic alcoholism presents with nystagmus, ataxia, and confusion. Thiamine is
administered before glucose. Why is this order important?
A. Thiamine prevents Wernicke encephalopathy from worsening
B. Glucose without thiamine precipitates acute psychosis
C. Glucose metabolism consumes thiamine, worsening deficiency
D. Thiamine alone treats hyperglycemia
🟢C
🔴 RATIONALE: Administering glucose before thiamine can precipitate or worsen Wernicke–Korsakoff
syndrome because thiamine is a cofactor for glucose metabolism; without it, lactate accumulates.
INSTANT DOWNLOAD PDF
Core Domains
General Principles (Biochemistry, Immunology, Genetics, Pharmacology)
Organ Systems (Cardiovascular, Respiratory, Renal, GI, Endocrine, Reproductive, Musculoskeletal, Neurology,
Psychiatry)
Hematology & Oncology
Microbiology & Infectious Diseases
Pathology & Pathophysiology
Behavioral Health & Social Sciences
Ethics, Legal Principles, & Patient Safety
Biostatistics & Epidemiology
Anatomy & Embryology
Physiology
Introduction
*This examination is designed to evaluate foundational medical knowledge required for USMLE Step 1. It
assesses your ability to integrate basic science principles with clinical presentations, diagnostic reasoning, and
patient management. Questions are formatted as single-best-answer multiple-choice items, often rooted in
clinical vignettes, to test real-world application and decision-making under time constraints. Emphasis is placed
on pathophysiologic mechanisms, pharmacologic interventions, ethical dilemmas, and evidence-based practice.
,Each question includes a verified correct answer and a concise rationale. Prepare to apply knowledge, not just
recall facts.*
SECTION ONE: QUESTIONS 1–100
Question 1
A 45-year-old man with hypertension presents with acute chest pain radiating to the jaw. ECG shows ST-
segment elevation in leads V2–V4. Which coronary artery is most likely occluded?
A. Right coronary artery
B. Left circumflex artery
C. Left anterior descending artery
D. Posterior descending artery
🟢C
🔴 RATIONALE: ST elevation in V2–V4 indicates an anterior wall myocardial infarction, most often caused by
occlusion of the left anterior descending artery.
Question 2
A 2-year-old child presents with failure to thrive, hepatosplenomegaly, and progressive neurodegeneration. A
lysosomal enzyme assay shows deficient beta-hexosaminidase A. Which substrate accumulates?
,A. Globotriaosylceramide
B. Sphingomyelin
C. GM2 ganglioside
D. Glucocerebroside
🟢C
🔴 RATIONALE: Beta-hexosaminidase A deficiency causes Tay–Sachs disease, leading to GM2 ganglioside
accumulation in neurons.
Question 3
A 68-year-old woman on warfarin for atrial fibrillation presents with acute onset of severe left lower extremity
pain, pallor, and pulselessness. Which laboratory finding is expected?
A. Elevated D-dimer
B. Prolonged PT and INR
C. Thrombocytopenia
D. Elevated factor VIII
🟢B
🔴 RATIONALE: The patient is already on warfarin (therapeutic INR), but acute arterial occlusion requires urgent
anticoagulation. The expected lab finding is prolonged PT/INR due to warfarin effect, not the cause of
embolism. Embolic source is likely cardiac.
Question 4
, A medical student accidentally sticks herself with a needle used on an HIV-positive patient. Which post-
exposure prophylaxis regimen is recommended within 72 hours?
A. Tenofovir disoproxil fumarate alone
B. Zidovudine monotherapy
C. Tenofovir disoproxil fumarate + emtricitabine plus raltegravir
D. Ritonavir-boosted lopinavir alone
🟢C
🔴 RATIONALE: Current CDC guidelines recommend a three-drug regimen (two NRTIs plus an integrase
inhibitor) for high-risk HIV exposures.
Question 5
A 55-year-old man with chronic alcoholism presents with nystagmus, ataxia, and confusion. Thiamine is
administered before glucose. Why is this order important?
A. Thiamine prevents Wernicke encephalopathy from worsening
B. Glucose without thiamine precipitates acute psychosis
C. Glucose metabolism consumes thiamine, worsening deficiency
D. Thiamine alone treats hyperglycemia
🟢C
🔴 RATIONALE: Administering glucose before thiamine can precipitate or worsen Wernicke–Korsakoff
syndrome because thiamine is a cofactor for glucose metabolism; without it, lactate accumulates.
