Acute Kidney Injury USMLE Step 1 Practice Question
A 52-year-old man with a history of hypertension presents with a 3-day history of productive cough, fever, and dyspnea. Chest imaging confirms pneumonia. On admission, his blood pressure is 88/52 mmHg, and he is started on broad-spectrum antibiotics, aggressive intravenous fluid resuscitation (6 liters over 12 hours), and norepinephrine. Despite these interventions, urine output decreases to 0.3 mL/kg/hr. Laboratory studies at 48 hours show: serum creatinine 3.5 mg/dL (baseline 0.9 mg/dL), BUN 68 mg/dL, urine osmolality 285 mOsm/kg, urine sodium 65 mEq/L, and fractional excretion of sodium (FENa) 3.2%. Urinalysis shows muddy brown casts. Which of the following best explains his acute kidney injury?
Answer choices
- APrerenal acute kidney injury from persistent hypoperfusion despite fluid resuscitation
- BPostrenal acute kidney injury from acute urinary retention
- CAcute tubular necrosis from sepsis-induced renal hypoperfusion and ischemiaCorrect answer
- DAcute interstitial nephritis from antibiotic-induced hypersensitivity reaction
- ERhabdomyolysis-associated acute kidney injury from critical illness myopathy
- FHepatorenal syndrome from occult cirrhosis and splanchnic vasodilation
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