Definition and Classification of Acute Kidney Injury

Abstract

Acute kidney injury (AKI) is the sudden loss of kidney function, typically developing over hours to days. Although AKI is easy to define conceptually, consensus operational definitions were unavailable until the early portion of the last decade. Three consensus definitions have been developed since 2002: the RIFLE (Risk, Injury, Failure, Loss, and End-stage) definition, developed by the Acute Dialysis Quality Initiative (ADQI), the Acute Kidney Injury Network (AKIN) definition and staging system, and most recently the Kidney Disease: Improving Global Outcomes (KDIGO) definition and staging system. Each of these definitions and staging systems is based on changes in serum creatinine and urine output. In the most current KDIGO definition, AKI is defined based on an absolute increase in serum creatinine of ≥0.3 mg/dL occurring within 48 h, a relative increase of ≥50% occurring within 7 days, or a urine output of <0.5 mL/kg per hour for more than 6 h. Progressive stages of AKI severity are defined by larger increases in serum creatinine, longer durations of oliguria or anuria, or need for renal replacement therapy. Although these definitions are useful in epidemiologic studies and clinical trials, their utility in clinical practice is uncertain.