Defining acute renal failure: RIFLE and beyond.

The introduction of the RIFLE classification has increased the conceptual understanding of the acute kidney injury (AKI) syndrome, and this classification has been successfully tested in a number of clinical studies. This review discusses the strengths and weaknesses of the RIFLE classification and suggests additional parameters to broaden future definitions of AKI. These definitions should not only focus on kidney function alone, but also include parameters describing the origin of the patient, the most important causal factors responsible for AKI and information on the pre-existing kidney function. This more complete definition should lead to a decrease in the variability of the results of epidemiological studies and of future clinical trials in AKI populations.