AKI KDIGO Staging Calculator for Acute Kidney Injury

About

The Kidney Disease: Improving Global Outcomes (KDIGO) AKI staging system was developed in 2012 as an international consensus classification to standardize the definition, staging, and management of acute kidney injury. It unified previous classification systems including RIFLE (2004) and AKIN (2007), resolving inconsistencies and providing a single evidence-based framework. KDIGO defines AKI as any of the following occurring within 7 days: increase in serum creatinine by ≥0.3 mg/dL (≥26.5 µmol/L) within 48 hours, increase in SCr to ≥1.5 times baseline within the prior 7 days, or urine volume <0.5 mL/kg/h for 6 hours. The staging system then classifies severity into three stages: Stage 1 (SCr 1.5-1.9x baseline or ≥0.3 mg/dL increase or UO <0.5 mL/kg/h for 6-12 hours), Stage 2 (SCr 2.0-2.9x baseline or UO <0.5 mL/kg/h for ≥12 hours), and Stage 3 (SCr 3.0x baseline or SCr ≥4.0 mg/dL or initiation of RRT or eGFR <35 mL/min/1.73m² in patients <18 years or UO <0.3 mL/kg/h for ≥24 hours or anuria ≥12 hours). This classification has been validated in over 100 million patient encounters worldwide and is associated with graded increases in mortality, length of stay, and risk of progression to chronic kidney disease.

Formula

Stage 1: SCr 1.5-1.9x baseline OR ≥0.3 mg/dL increase OR UO <0.5 mL/kg/h 6-12h | Stage 2: SCr 2.0-2.9x baseline OR UO <0.5 mL/kg/h ≥12h | Stage 3: SCr 3.0x baseline OR SCr ≥4.0 mg/dL OR RRT OR eGFR <35 in <18yrs OR UO <0.3 mL/kg/h ≥24h OR anuria ≥12h

The KDIGO AKI staging is based on the worst of either serum creatinine or urine output criteria. Stage 1 requires SCr 1.5-1.9 times baseline or an absolute increase of ≥0.3 mg/dL within 48 hours, or urine output <0.5 mL/kg/h for 6-12 hours. Stage 2 requires SCr 2.0-2.9 times baseline or urine output <0.5 mL/kg/h for ≥12 hours. Stage 3 requires SCr 3.0 times baseline, SCr ≥4.0 mg/dL (with an acute increase of ≥0.5 mg/dL), initiation of renal replacement therapy, or in patients <18 years, eGFR <35 mL/min/1.73m², or urine output criteria: <0.3 mL/kg/h for ≥24 hours or anuria for ≥12 hours. If RRT is initiated, the patient is automatically classified as Stage 3 regardless of other criteria.

Score Interpretation

The KDIGO AKI staging system is the international standard for classifying acute kidney injury severity and is endorsed by the KDIGO organization, the Acute Disease Quality Initiative (ADQI), and national nephrology societies worldwide. AKI affects approximately 10-15% of hospitalized patients and over 50% of ICU patients, with even transient AKI associated with increased mortality and long-term renal sequelae. The staging system directly guides management: Stage 1 prompts close monitoring and removal of nephrotoxic agents; Stage 2 triggers nephrology consultation; Stage 3 necessitates evaluation for renal replacement therapy. Importantly, the staging system uses the worst of creatinine or urine output criteria, as each provides complementary prognostic information. Studies have demonstrated a stepwise increase in mortality with each AKI stage: Stage 1 (OR 2.2), Stage 2 (OR 6.1), and Stage 3 (OR 8.6) compared to patients without AKI. The system also identifies patients at risk for progression to CKD — even a single AKI episode increases the risk of de novo CKD by 10-fold. Early nephrology consultation has been shown to reduce mortality and improve renal recovery rates, particularly in Stage 2 and 3 AKI.

Reference Ranges