KDIGO Clinical Criteria for AKI Staging
The KDIGO classification uses three clinical criteria to stage AKI: (1) serum creatinine changes, (2) urine output measurements, and (3) need for renal replacement therapy. 1
The Three Core Clinical Criteria
1. Serum Creatinine (SCr) Changes
The KDIGO system defines AKI stages based on the magnitude of creatinine elevation from baseline 1:
- Stage 1: SCr increase of 1.5-1.9 times baseline OR absolute increase ≥0.3 mg/dL (≥26.5 μmol/L) 1
- Stage 2: SCr increase of 2.0-2.9 times baseline 1
- Stage 3: SCr increase ≥3.0 times baseline OR SCr ≥4.0 mg/dL (≥353.6 μmol/L) with an acute increase of ≥0.3 mg/dL OR initiation of renal replacement therapy 1
The creatinine criteria use differential timing: a 48-hour window for the 0.3 mg/dL absolute increase and a 7-day window for relative increases from baseline 1, 2.
2. Urine Output (UO) Measurements
Urine output criteria provide parallel staging independent of creatinine 1:
- Stage 1: UO <0.5 mL/kg/h for 6-12 hours 1
- Stage 2: UO <0.5 mL/kg/h for ≥12 hours 1
- Stage 3: UO <0.3 mL/kg/h for ≥24 hours OR anuria for ≥12 hours 1
Important caveat: Urine output criteria are generally applicable only in intensive care settings where accurate monitoring is feasible, and should not be relied upon in patients receiving diuretics or those with cirrhosis and ascites 2, 3.
3. Renal Replacement Therapy (RRT)
Initiation of RRT automatically classifies the patient as Stage 3 AKI, regardless of creatinine or urine output values 1. In patients <18 years, a decrease in eGFR to <35 mL/min/1.73 m² also defines Stage 3 1.
Staging Algorithm
Patients are staged according to the highest severity criterion met, whether by creatinine, urine output, or RRT need 1. The staging is performed retrospectively when the episode is complete, though early detection should occur in real-time based on initial marker changes 2, 3.
Clinical Significance and Validation
The KDIGO criteria have been independently validated in multiple studies and demonstrate strong correlation between stage progression and mortality 1, 2. Even Stage 1 AKI (particularly the 0.3 mg/dL creatinine increase) is independently associated with approximately four-fold increased hospital mortality 1. Research shows that when patients meet both creatinine and urine output criteria simultaneously, outcomes are significantly worse than when meeting only one criterion 4.
Common Pitfalls to Avoid
Do not wait for creatinine to reach 1.5 mg/dL before diagnosing AKI, as this outdated threshold often indicates GFR has already fallen to approximately 30 mL/min 3. Monitor temporal changes at 48-hour intervals to detect the 0.3 mg/dL threshold early 3.
In patients with cirrhosis and ascites, focus exclusively on serum creatinine changes rather than urine output, as these patients are frequently oliguric with avid sodium retention despite maintaining relatively normal GFR 3. A creatinine threshold of ≥1.5 mg/dL predicts AKI progression and worse prognosis in this population 3.
Note: You did not provide specific patient data (baseline creatinine, current creatinine, urine output measurements, or clinical context), so I cannot determine what stage this patient is at. To stage the patient, apply the criteria above to their specific laboratory values and clinical parameters.