A 70-year-old male is admitted for pneumonia. On day 3, his creatinine rises from a baseline of 1.0 mg/dL to 2.5 mg/dL. He is oliguric. Urine osmolality is 350 mOsm/kg, urine sodium is 45 mEq/L, and fractional excretion of sodium (FENa) is 2.5%. What is the most likely cause of his acute kidney injury?

The correct answer to the question "A 70-year-old male is admitted for pneumonia. On day 3, his creatinine rises from a baseline of 1.0 mg/dL to 2.5 mg/dL. He is oliguric. Urine osmolality is 350 mOsm/kg, urine sodium is 45 mEq/L, and fractional excretion of sodium (FENa) is 2.5%. What is the most likely cause of his acute kidney injury?" is Option B: Acute tubular necrosis.

The other options — A) Prerenal azotemia, C) Postrenal obstruction, D) Acute interstitial nephritis — are incorrect for this USMLE Exam Prep question. As explained above: The laboratory findings, specifically a fractional excretion of sodium (FENa) greater than 2%, urine sodium greater than 20 mEq/L, and relatively low urine osmolality, are characteristic of acute tub…