Development of standardized acute kidney injury (AKI) definitions and staging criteria have led to an appreciation of the association between AKI and poor outcomes in children with heart disease.2–5 The evolution of these definitions and criteria have culminated in a harmonized construct from the Kidney Disease Improving Global Outcomes (KDIGO) AKI Work Group (Table 78.2) As noted above, the critical clinical and epidemiologic advance from a standardized AKI definition and staging criteria has been the realization that even the doubling of serum creatinine or 12 hours of oliguria are associated with morbidity and mortality in children.6 Table 78.2 Kidney Disease Improving Global Outcomes Acute Kidney Injury Work Group Criteria Serum Creatinine Criteria Increase by ≥0.3 mg/dL within 48 h or Increase to 1.5 times baseline, which is known or presumed to have occurred within the prior 7 days Stage 1.5–1.9 times baseline or Stage ≥0.3 mg/dL increase 2.0–2.9 times baseline Stage 3.0 times baseline or Increase in plasma creatinine to ≥4.0 mg/dL or Initiation of renal replacement therapya or In patients age