KDIGO Definition and Diagnostic Criteria for Acute Kidney Injury

Definition of AKI

• KDIGO defines acute kidney injury as an increase in serum creatinine to ≥ 1.5 times the baseline that is known or presumed to have occurred within the prior 7 days. 1

Diagnostic Criteria (any one must be met)

• Serum creatinine rise ≥ 0.3 mg/dL (≥ 26.5 µmol/L) within 48 hours. 1
• Serum creatinine rise to ≥ 1.5 times baseline within the preceding 7 days. 1
• Urine output < 0.5 mL/kg/hour for ≥ 6 consecutive hours. 1

Baseline Creatinine Estimation When Unavailable

• When no prior creatinine is available, KDIGO recommends back‑calculating the baseline using the MDRD equation and assuming an estimated GFR of 75 mL/min/1.73 m². 2

Clinical Significance of Small Creatinine Increases

• An absolute increase of ≥ 0.3 mg/dL in serum creatinine independently raises mortality risk by roughly four‑fold, highlighting the prognostic importance of the 48‑hour criterion. 2