A 60-year-old female is hospitalized for community-acquired pneumonia. On hospital day 3, she develops acute kidney injury with a creatinine rise from 0.8 mg/dL to 2.5 mg/dL. Her urine output has decreased, and her urine sodium is 55 mEq/L, and fractional excretion of sodium (FENa) is 3%. She is receiving IV antibiotics and has stable hemodynamics. What is the most likely cause of her AKI?
✓ Correct Answer: Option B
A high urine sodium (>40 mEq/L) and FENa >2% in the setting of AKI strongly indicate intrinsic kidney injury, specifically acute tubular necrosis (ATN). This often results from sepsis or nephrotoxins like antibiotics. Prerenal azotemia would present with low urine sodium and FENa.