A 70-year-old man is admitted for acute kidney injury. His urine output is low, and his serum creatinine has doubled in 24 hours. Urine osmolality is 600 mOsm/kg, urine sodium is 10 mEq/L, and fractional excretion of sodium (FENa) is 0.5%. What is the most likely etiology of his AKI?
✓ Correct Answer: Option B
The urine osmolality >500 mOsm/kg, urine sodium <20 mEq/L, and FENa <1% are classic findings for prerenal azotemia. These indicate intact tubular function attempting to reabsorb sodium and water in response to hypoperfusion.