The KDIGO (Kidney Disease: Improving Global Outcomes) AKI staging system was published in 2012 to provide a unified, internationally standardised definition and classification of acute kidney injury. Prior to KDIGO, inconsistent AKI definitions (RIFLE, AKIN) led to challenges in comparing study populations. KDIGO defined AKI as any of: increase in serum creatinine by ≥0.3 mg/dL within 48 hours, increase to ≥1.5× baseline within 7 days, or urine output <0.5 mL/kg/hour for ≥6 hours. Even small creatinine rises (Stage 1) independently predict mortality and hospital length of stay.