A 65-year-old man post-cardiac surgery develops oliguric AKI. Serum creatinine rises from 1.0 to 3.8 mg/dL over 48 hours. Urine output is 0.3 mL/kg/hr. By KDIGO AKI classification, this is:

• A AKI Stage 3 ✓
• B AKI Stage 1
• C AKI Stage 2
• D AKI Stage 2 by creatinine, Stage 1 by urine output

Explanation

KDIGO 2012 AKI staging: Stage 1 = creatinine ×1.5–1.9× baseline or rise ≥0.3 mg/dL within 48 hrs, or UO <0.5 mL/kg/hr for 6–12 hrs. Stage 2 = creatinine ×2.0–2.9× baseline or UO <0.5 mL/kg/hr for ≥12 hrs. Stage 3 = creatinine ×3.0× baseline, or creatinine ≥4.0 mg/dL, or RRT initiation, or UO <0.3 mL/kg/hr for ≥24 hrs (or anuria ≥12 hrs). This patient: creatinine from 1.0 to 3.8 = ×3.8 baseline AND creatinine ≥4.0 mg/dL threshold approached, meeting Stage 3 criteria by creatinine. UO <0.5 mL/kg/hr fits Stage 2 by output; the higher stage is applied when criteria overlap — Stage 3 is the final designation.

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

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