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ACUTE kidney injury (AKI) is a complex and common clinical disorder in both human and veterinary medicine. Patients with AKI show differing clinical manifestations that range from a slight increase in serum creatinine to severe renal failure that characteristically portends high mortality. It is therefore important to determine prognosis following AKI in epidemiological studies. However, because of the lack of a universal standard classification for AKI, the severity of AKI remains controversial. In human medicine, mortality due to AKI has been reported to vary widely between studies ( Liano and Pascual 1996 , Silvester and others 2001 , Bagshaw and others 2005 ), and the results of similar studies in veterinary medicine have led to differing conclusions ( Behrend and others 1996 , Vaden and others 1997 ). Recently, a study in human beings was conducted to establish a uniform standard for AKI diagnosis and classification in order to allow better management of patients. A multi-level classification system was developed by the Acute Dialysis Quality Initiative (ADQI) working group ( Bellomo and others 2004 ). The system is known as RIFLE ( Bellomo and others 2004 ), with the acronym indicating Risk of renal dysfunction, Injury to the kidney, Failure of renal function, Loss of renal function and End-stage renal disease ( Table 1 ). This multi-level system simultaneously classified the renal function of patients into three classes of severity: those in whom renal function was mildly affected (Risk class), those in whom renal dysfunction was marked (Injury class), and those in whom renal damage was severe (Failure class). Both sensitivity and specificity were considered when evaluating a wide range of renal diseases. RIFLE criteria were simple and easy to apply to clinical cases. To date, several studies have shown the validity of using RIFLE criteria when classifying AKI with regard to both severity and outcome ( Hoste and others 2006 , Uchino and others 2006 , Bagshaw and others 2008 , Ricci and others 2008 ).
RIFLE category | Serum creatinine criteria | Urine output criteria | Modified criteria |
Risk | ≥1.5-fold from serum creatinine baseline or 50% to 25% decrease in GFR | <0.5 ml/kg/h for ≥6 hours | Creatinine 116-174 µmol/l |
Injury | ≥2.0-fold from serum creatinine baseline or 75% to 50% decrease in GFR | <0.5 ml/kg/h for ≥12... |