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Acute Tubular Necrosis — RACP Adult Medicine MCQ

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ModerateNephrologyAcute Tubular NecrosisRACP Adult Medicine

A 55-year-old woman develops AKI after receiving IV contrast for CT angiography. Creatinine rises from 100 to 280 μmol/L over 72 hours. Urine Na⁺ is 55 mmol/L. FeNa is 3.5%. Urine microscopy shows muddy brown granular casts. Urine output is 200 mL/day. What is the most likely type of AKI?

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Correct answer: A — Intrinsic renal (ATN)

Elevated urine sodium (>40 mmol/L), FeNa >2%, muddy brown granular casts on urine microscopy, and oliguria after nephrotoxic exposure (IV contrast) is acute tubular necrosis (ATN) — the most common cause of intrinsic AKI. The damaged tubules cannot reabsorb sodium (hence high urine Na and FeNa). Treatment is supportive: avoid further nephrotoxins, optimise volume, and dialysis if indicated.

Reference: KDIGO – 2024 – AKI; eTG Nephrology 2024