Defining acute kidney injury: what is the most appropriate metric?

Glomerular filtration rate (GFR) is the most widely accepted measure of kidney function. Acute kidney injury (AKI) is defined as a reduction in GFR. GFR is, however, rarely measured in clinical practice; instead, serum markers (primarily creatinine) are used to define AKI. Because serum creatinine level is not linearly related to GFR, the performance of this marker is associated with ascertainment bias and poor sensitivity. In this article we discuss the limitations and pitfalls of using serum markers to define AKI, and offer some suggestions for the future.