Acute Kidney Injury (AKI) Diagnosis, Classification, and Staging

Authored by Sourabh Sharma, published on 2026-11-12 16:05:15.0

Suspected Acute Deterioration in Kidney Function
- Hemodynamic Instability or Life-Threatening AKI Complication?
  - Stabilize; Treat Emergencies; Obtain Urgent ICU and Nephrology Support
  - Measure Serial SCr and Weight-Based UO; Establish Baseline Kidney Function
    - SCr ≥0.3 mg/dL/48 Hours, ≥1.5×/7 Days, or UO <0.5 mL/kg/h for 6 Hours?
      - No Confirmed AKI: Repeat SCr/UO and Evaluate AKD, CKD, and Alternatives
      - Assign the Highest KDIGO Stage Met by SCr or UO
        
        Stage 1: SCr 1.5–1.9× or ≥0.3 mg/dL Rise; UO <0.5 mL/kg/h for 6–12 Hours
        
        Refractory Hyperkalemia, Acidosis, Fluid Overload, Uremic Complication, or Dialyzable Toxin?
        
        Start Urgent KRT With Nephrology and Critical Care Support
        
        Assess Volume, Hemodynamics, Drugs, Nephrotoxins, Urinalysis, Microscopy, and Biochemistry; Determine Cause
        
        Restore Effective Circulation and Correct Hemodynamic Drivers
        
        Treat Cause, Stop Nephrotoxins, Adjust Renally Cleared Drugs, and Manage Complications
        
        Reassess Serial SCr, UO, Peak Stage, Complications, and Kidney Recovery
        
        Escalate Nephrology; Reassess Cause, Imaging, Biopsy, and KRT Need
        
        Document Recovery and Arrange Post-AKI Kidney Follow-Up
        
        Classify as AKD; Continue Evaluation and Nephrology Follow-Up
        
        Classify as CKD; Identify Superimposed AKI or AKD
        
        Obtain Urgent Renal Ultrasound; Relieve Obstruction and Refer Urology
        
        Treat Cause, Stop Nephrotoxins, Adjust Renally Cleared Drugs, and Manage Complications
        
        Reassess Serial SCr, UO, Peak Stage, Complications, and Kidney Recovery
        
        Escalate Nephrology; Reassess Cause, Imaging, Biopsy, and KRT Need
        
        Document Recovery and Arrange Post-AKI Kidney Follow-Up
        
        Classify as AKD; Continue Evaluation and Nephrology Follow-Up
        
        Classify as CKD; Identify Superimposed AKI or AKD
        
        Target Glomerular, Tubulointerstitial, Tubular, and Vascular Causes; Refer for Biopsy When Indicated
        
        Treat Cause, Stop Nephrotoxins, Adjust Renally Cleared Drugs, and Manage Complications
        
        Reassess Serial SCr, UO, Peak Stage, Complications, and Kidney Recovery
        
        Escalate Nephrology; Reassess Cause, Imaging, Biopsy, and KRT Need
        
        Document Recovery and Arrange Post-AKI Kidney Follow-Up
        
        Classify as AKD; Continue Evaluation and Nephrology Follow-Up
        
        Classify as CKD; Identify Superimposed AKI or AKD
        
        Stage 2: SCr 2.0–2.9×; UO <0.5 mL/kg/h for ≥12 Hours
        
        Refractory Hyperkalemia, Acidosis, Fluid Overload, Uremic Complication, or Dialyzable Toxin?
        
        Start Urgent KRT With Nephrology and Critical Care Support
        
        Assess Volume, Hemodynamics, Drugs, Nephrotoxins, Urinalysis, Microscopy, and Biochemistry; Determine Cause
        
        Restore Effective Circulation and Correct Hemodynamic Drivers
        
        Treat Cause, Stop Nephrotoxins, Adjust Renally Cleared Drugs, and Manage Complications
        
        Reassess Serial SCr, UO, Peak Stage, Complications, and Kidney Recovery
        
        Escalate Nephrology; Reassess Cause, Imaging, Biopsy, and KRT Need
        
        Document Recovery and Arrange Post-AKI Kidney Follow-Up
        
        Classify as AKD; Continue Evaluation and Nephrology Follow-Up
        
        Classify as CKD; Identify Superimposed AKI or AKD
        
        Obtain Urgent Renal Ultrasound; Relieve Obstruction and Refer Urology
        
        Treat Cause, Stop Nephrotoxins, Adjust Renally Cleared Drugs, and Manage Complications
        
        Reassess Serial SCr, UO, Peak Stage, Complications, and Kidney Recovery
        
        Escalate Nephrology; Reassess Cause, Imaging, Biopsy, and KRT Need
        
        Document Recovery and Arrange Post-AKI Kidney Follow-Up
        
        Classify as AKD; Continue Evaluation and Nephrology Follow-Up
        
        Classify as CKD; Identify Superimposed AKI or AKD
        
        Target Glomerular, Tubulointerstitial, Tubular, and Vascular Causes; Refer for Biopsy When Indicated
        
        Treat Cause, Stop Nephrotoxins, Adjust Renally Cleared Drugs, and Manage Complications
        
        Reassess Serial SCr, UO, Peak Stage, Complications, and Kidney Recovery
        
        Escalate Nephrology; Reassess Cause, Imaging, Biopsy, and KRT Need
        
        Document Recovery and Arrange Post-AKI Kidney Follow-Up
        
        Classify as AKD; Continue Evaluation and Nephrology Follow-Up
        
        Classify as CKD; Identify Superimposed AKI or AKD
        
        Stage 3: SCr ≥3× Baseline or ≥4.0 mg/dL With Acute Rise; KRT; UO <0.3 ≥24h or Anuria ≥12h
        
        Refractory Hyperkalemia, Acidosis, Fluid Overload, Uremic Complication, or Dialyzable Toxin?
        
        Start Urgent KRT With Nephrology and Critical Care Support
        
        Assess Volume, Hemodynamics, Drugs, Nephrotoxins, Urinalysis, Microscopy, and Biochemistry; Determine Cause
        
        Restore Effective Circulation and Correct Hemodynamic Drivers
        
        Treat Cause, Stop Nephrotoxins, Adjust Renally Cleared Drugs, and Manage Complications
        
        Reassess Serial SCr, UO, Peak Stage, Complications, and Kidney Recovery
        
        Escalate Nephrology; Reassess Cause, Imaging, Biopsy, and KRT Need
        
        Document Recovery and Arrange Post-AKI Kidney Follow-Up
        
        Classify as AKD; Continue Evaluation and Nephrology Follow-Up
        
        Classify as CKD; Identify Superimposed AKI or AKD
        
        Obtain Urgent Renal Ultrasound; Relieve Obstruction and Refer Urology
        
        Treat Cause, Stop Nephrotoxins, Adjust Renally Cleared Drugs, and Manage Complications
        
        Reassess Serial SCr, UO, Peak Stage, Complications, and Kidney Recovery
        
        Escalate Nephrology; Reassess Cause, Imaging, Biopsy, and KRT Need
        
        Document Recovery and Arrange Post-AKI Kidney Follow-Up
        
        Classify as AKD; Continue Evaluation and Nephrology Follow-Up
        
        Classify as CKD; Identify Superimposed AKI or AKD
        
        Target Glomerular, Tubulointerstitial, Tubular, and Vascular Causes; Refer for Biopsy When Indicated
        
        Treat Cause, Stop Nephrotoxins, Adjust Renally Cleared Drugs, and Manage Complications
        
        Reassess Serial SCr, UO, Peak Stage, Complications, and Kidney Recovery
        
        Escalate Nephrology; Reassess Cause, Imaging, Biopsy, and KRT Need
        
        Document Recovery and Arrange Post-AKI Kidney Follow-Up
        
        Classify as AKD; Continue Evaluation and Nephrology Follow-Up
        
        Classify as CKD; Identify Superimposed AKI or AKD
Do Not Diagnose or Stage AKI From Isolated Urea or eGFR
Critical Illness: Verify Catheter Patency, Track Hourly UO, and Trend SCr Frequently
Unknown Baseline or CKD: Use Prior Stable SCr, Serial Trends, and UO; Apply Standard Staging

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