A 70-year-old man is admitted for hypotension and dehydration secondary to severe gastroenteritis. His creatinine has risen from a baseline of 1.0 mg/dL to 2.5 mg/dL. Urinalysis shows a specific gravity of 1.028, no protein, no cells, and occasional hyaline casts. Fractional excretion of sodium (FENa) is 0.5%. What is the most likely diagnosis?

The correct answer to the question "A 70-year-old man is admitted for hypotension and dehydration secondary to severe gastroenteritis. His creatinine has risen from a baseline of 1.0 mg/dL to 2.5 mg/dL. Urinalysis shows a specific gravity of 1.028, no protein, no cells, and occasional hyaline casts. Fractional excretion of sodium (FENa) is 0.5%. What is the most likely diagnosis?" is Option C: Pre-renal acute kidney injury.

The other options — A) Acute tubular necrosis, B) Post-renal obstruction, D) Acute interstitial nephritis — are incorrect for this USMLE Exam Prep question. As explained above: Pre-renal AKI is characterized by decreased renal perfusion. Findings like elevated specific gravity, low FENa (