A 55-year-old diabetic patient develops AKI post-contrast CT. Serum creatinine rises from 1.2 mg/dL to 1.9 mg/dL within 48 hours. FENa is 0.4%, urine sodium 12 mEq/L, urine osmolality 520 mOsm/kg. Which pattern of injury does this MOST likely represent?

• A Contrast-induced nephropathy with tubular injury (ATN pattern)
• B Pre-renal AKI with preserved tubular function ✓
• C Cholesterol embolism syndrome
• D Acute interstitial nephritis from contrast media

Explanation

FENa <1% with urine sodium <20 mEq/L and high urine osmolality (>500 mOsm/kg) indicates preserved tubular concentration ability suggesting a pre-renal pattern, where tubules are functionally intact and actively reabsorbing sodium and water. True contrast-induced nephropathy causing ATN would show FENa >2%, urine sodium >40 mEq/L (tubular dysfunction), and muddy brown casts. This early post-contrast rise in creatinine with pre-renal indices may simply reflect volume depletion from contrast osmotic diuresis or inadequate hydration rather than direct tubular toxicity.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.