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The USMLE exam has 280 questions and runs 8 hours.
These 10 free USMLE questions are organized by exam domain, so you can see how each part of the United States Medical Licensing Examination Step 1 (USMLE Step 1) blueprint is tested. Reveal the answer and explanation under each question.
At an 18-month well-child visit, a boy runs with a slightly stiff gait, feeds himself with a spoon, uses 14 single words, engages in simple pretend play, and plays alongside rather than cooperatively with other children. He does not yet combine words. Which assessment is most accurate?
Correct answer: B - Development is age-appropriate; spontaneous 2-word phrases are expected by 24 months
A 6-year-old boy has recurrent Serratia marcescens lymphadenitis and Aspergillus pneumonia. Neutrophils fail to increase fluorescence on a dihydrorhodamine assay after stimulation. Which neutrophil reaction is defective?
Correct answer: C - Generation of superoxide from molecular oxygen
A 43-year-old woman develops fluctuating confusion, fever, petechiae, and acute kidney injury. Hemoglobin is 8.4 g/dL, platelet count is 18,000/mm3, lactate dehydrogenase is elevated, and the blood smear shows schistocytes. Prothrombin time and activated partial thromboplastin time are normal. What is the underlying mechanism?
Correct answer: A - Deficient cleavage of ultra-large von Willebrand factor multimers because ADAMTS13 activity is low
A 35-year-old woman taking sertraline begins linezolid for a resistant infection. Eight hours later, she has fever, agitation, diaphoresis, diarrhea, and tremor. Which additional examination finding would most strongly support serotonin syndrome rather than neuroleptic malignant syndrome?
Correct answer: D - Inducible ankle clonus with hyperreflexia
A 67-year-old man suddenly develops vertigo, vomiting, hoarseness, dysphagia, left-sided ptosis and miosis, loss of pain and temperature sensation on the left face and right body, and left limb ataxia. The infarct most likely involves which artery?
Correct answer: B - Posterior inferior cerebellar artery
Shortly after induction of anesthesia with sevoflurane and succinylcholine, a patient develops rapidly rising end-tidal carbon dioxide, generalized muscle rigidity, hyperkalemia, acidosis, and hyperthermia. Dantrolene treats this condition by which action?
Correct answer: A - Inhibiting RYR1-mediated calcium release from the sarcoplasmic reticulum
Three days after an inferoposterior myocardial infarction, a patient develops abrupt hypotension and pulmonary edema. Examination reveals a new holosystolic murmur loudest at the apex, and pulmonary capillary wedge tracing shows giant V waves. Which structure has most likely ruptured?
Correct answer: C - Posteromedial papillary muscle
A 2-year-old child with tetralogy of Fallot becomes deeply cyanotic while playing and instinctively squats. Which change produced by squatting most directly improves this child's oxygenation?
Correct answer: D - Increased systemic resistance that reduces right-to-left shunting
A 64-year-old man with a 50-pack-year smoking history has progressive exertional dyspnea. Pulmonary function testing shows FEV1 42% predicted, FVC 78% predicted, FEV1/FVC 0.43, total lung capacity 128% predicted, and diffusing capacity 44% predicted. Which structural abnormality best explains the reduced diffusing capacity?
Correct answer: A - Destruction of alveolar septa and the pulmonary capillary bed
An 8-year-old boy develops periorbital edema, cola-colored urine, and hypertension 2 weeks after impetigo. Urinalysis shows dysmorphic erythrocytes and red-cell casts, and serum C3 is low. Which electron-microscopic finding is most likely?
Correct answer: C - Subepithelial electron-dense humps
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