Defining and classifying AKI: one set of criteria.

Over the last several years there have been consistent calls for a consensus definition and classification system for the syndrome now known as acute kidney injury (AKI) [1,2]. The major aim of such a system, it was argued, would be to bring this major intensive care syndrome to a standard of definition and a level of classification similar to that achieved by other common ICU syndromes (e.g. sepsis and acute lung injury). Following such advocacy and through the persistent work of the Acute Dialysis Quality Initiative (ADQI) group, such a system was developed through a broad consensus of experts [3]. The classification system that resulted is the RIFLE criteria, an acronym for three levels of severity: risk, injury and failure, and two outcomes: persistent acute renal failure termed loss and end-stage kidney disease. RIFLE was initially greeted with skepticism by both the critical care and nephrology communities. Concern was raised over the use of very small alterations in the serum creatinine and urine output and some objected to the use of an acronym instead of the numerical stages used in chronic kidney disease. Interestingly, others were concerned that a 50% increase in serum creatinine was too conservative and sought to demonstrate that even smaller changes were important [4]. However, the original publication of the RIFLE criteria has now been accessed more than 100 000 times [5] and RIFLE has become the most widely used definition of acute renal failure in both the critical care and nephrology literature [6–10]. The total number of patients included in studies validating RIFLE now exceeds 200 000. Thus, the goal of standardizing a definition and classification system for one of the most common ICU syndromes would appear to have been realized. However, standards do