Acute Kidney Injury USMLE Step 1 Practice Question
A 78-year-old woman with poor oral intake for 3 days presents with hypotension (BP 88/52), tachycardia (HR 110), and oliguria. Serum creatinine is 2.8 mg/dL (baseline 0.9), BUN 48 mg/dL, with BUN/Cr ratio of 17:1. Urinalysis shows no proteinuria, casts, or hematuria. She takes no nephrotoxic medications. Which finding most supports prerenal azotemia rather than intrinsic acute tubular necrosis?
Answer choices
- AUrine sodium greater than 40 mEq/L
- BBUN to creatinine ratio greater than 20 to 1Correct answer
- CLoss of medullary concentrating gradient from tubular injury
- DFractional excretion of sodium greater than 2 percent
- EMuddy brown granular casts
- FPresence of large epithelial cells and white blood cell casts in the urine
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