KDIGO AKI Staging
KDIGO AKI staging classifies acute kidney injury severity into Stages 1–3 based on serum creatinine changes from baseline and/or urine output criteria. The higher of the two criteria determines the stage.
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✓ when to use
Apply to any hospitalised patient with suspected or confirmed AKI. Stage guides monitoring intensity, nephrology referral timing, and consideration of renal replacement therapy. AKI is defined as any one of: creatinine increase ≥26.5 µmol/L within 48h, creatinine ≥1.5× baseline within 7 days, or urine output <0.5 mL/kg/h for 6h.
✗ when not to use
KDIGO AKI staging requires knowledge of baseline creatinine, which may not be available. If unknown, the lowest creatinine during the admission or an estimated baseline from eGFR can be used, but this introduces uncertainty. Staging does not identify the cause of AKI — aetiology assessment (prerenal, intrinsic, post-renal) is a separate clinical task.
clinical pearls
- AKI is defined by EITHER creatinine OR urine output criteria — you do not need both. In practice, creatinine-based diagnosis is more common because urine output monitoring requires catheterisation and hourly measurement.
- Baseline creatinine is the most important but often the most uncertain value. Use the most recent stable outpatient creatinine from the past 3–12 months. If unavailable, a back-calculated baseline assuming eGFR 75 mL/min/1.73m² can be used as a pragmatic estimate.
- AKI Stage 3 includes any patient started on renal replacement therapy (RRT), regardless of creatinine or urine output values at the time.
- The 48-hour and 7-day windows are important: an increase of ≥26.5 µmol/L must occur within 48 hours, while the 1.5× baseline criterion can develop over up to 7 days. These are different diagnostic windows for different patterns of AKI.
- All patients with AKI should have their medications reviewed: stop/hold nephrotoxins (NSAIDs, ACEi/ARBs in haemodynamic instability, aminoglycosides, metformin in Stage 2+), adjust renally cleared drug doses, and avoid contrast unless essential.