Cruz and colleagues [1] have called appropriately for a reappraisal of RIFLE and AKIN and have thoughtfully detailed many of the issues with these progressive consensus definitions of acute kidney injury (AKI) and with the ways in which they have been applied. They see the elimination of the glomerular filtration rate (GFR) criteria from the AKIN definition as serendipitously discouraging the incorrect use of changes in estimated GFR for AKI diagnosis. We note that it also serendipitously removed the errors in degree of GFR change of the RIFLE R and F criteria definitions compared to the percentage change in creatinine [2]. Nevertheless, we would argue that further refinement of AKI definitions should allow for optional measured changes in GFR to await the possibility that real-time measures of GFR become available. After all, creatinine is merely a surrogate marker for GFR and a poor one at that. Furthermore, the incremental ‘creatinine creep’ type of AKI (0.1 mg/dl/day) illustrated by the authors might then be quickly revealed as incremental injury and loss of GFR.