KDIGO Definition of Acute Kidney Injury
According to KDIGO guidelines, AKI is correctly defined as an increase in serum creatinine of ≥1.5 times baseline within the prior 7 days, making option 4 the correct answer. 1
Complete KDIGO Diagnostic Criteria
The KDIGO definition requires meeting any one of the following three criteria: 1
- Serum creatinine increase ≥0.3 mg/dL within 48 hours, OR 1
- Serum creatinine increase to ≥1.5 times baseline (which is known or presumed to have occurred within the prior 7 days), OR 1
- Urine output <0.5 mL/kg/hour for 6 consecutive hours 1
Why the Other Options Are Incorrect
Option 1: "Decrease in urine creatinine level of <500 mg/day"
- This is completely incorrect - AKI diagnosis does not involve measuring urine creatinine levels at all 1
- The confusion may stem from proteinuria criteria (>500 mg/day suggests glomerular disease), but this is not part of AKI definition 2
Option 2: "Decrease in urine output of <1 mg/kg/hour in the last 12 hours"
- This is incorrect on multiple counts 1
- The correct urine output criterion is <0.5 mL/kg/hour (not 1 mg/kg/hour - wrong units and wrong threshold) 1
- The duration for Stage 1 AKI is 6 hours, not 12 hours 1
- Note: <0.5 mL/kg/hour for ≥12 hours defines Stage 2 AKI 2, 3
Option 3: "Increase in serum creatinine level of >0.5 mg/dL"
- This is incorrect - the absolute increase threshold is ≥0.3 mg/dL within 48 hours, not >0.5 mg/dL 1
- This criterion is time-dependent (must occur within 48 hours) 1
Option 5: "Increase in urine output of >0.5/min/hour for at least 6 hours"
- This is completely backwards - AKI is defined by a decrease in urine output, not an increase 1
Critical Clinical Caveats
Baseline creatinine determination: When no baseline exists, back-calculate using the MDRD equation assuming a GFR of 75 mL/min/1.73 m² 1, 2
Volume status effects: Serum creatinine can be diluted by massive fluid resuscitation, potentially masking significant GFR reduction and delaying AKI diagnosis 1, 2
Urine output limitations: In cirrhotic patients with ascites, urine output criteria are unreliable due to avid sodium retention despite relatively normal GFR - focus exclusively on serum creatinine changes in this population 2, 3
Clinical significance: Even small creatinine increases (≥0.3 mg/dL) independently increase mortality approximately four-fold, emphasizing the importance of the 48-hour absolute criterion 2, 4