A 58-year-old male develops acute kidney injury after a diarrheal illness. His BUN is 60 mg/dL, creatinine is 3.5 mg/dL. Urine sodium is 8 mEq/L and fractional excretion of sodium (FENa) is 0.4%. Which of the following is the most likely cause of his AKI?

The correct answer to the question "A 58-year-old male develops acute kidney injury after a diarrheal illness. His BUN is 60 mg/dL, creatinine is 3.5 mg/dL. Urine sodium is 8 mEq/L and fractional excretion of sodium (FENa) is 0.4%. Which of the following is the most likely cause of his AKI?" is Option B: Prerenal azotemia..

The other options — A) Acute tubular necrosis (ATN)., C) Acute interstitial nephritis (AIN)., D) Postrenal obstruction. — are incorrect for this USMLE Exam Prep question. As explained above: Prerenal azotemia, caused by decreased renal perfusion (e.g., from diarrheal illness), is characterized by the kidney's attempt to conserve sodium and water. This results in a low urine sodium (