More Evidence that Cystatin C Predicts Mortality Better than Creatinine

Abstract

The main clinical benefit of estimating renal function in the general population is to identify and treat patients at risk for developing ESRD, cardiovascular events, and death.1 Unfortunately, the most widely used equations to estimate GFR are limited, in part, by their reliance on serum creatinine as the filtration marker (estimated GFR [eGFR]). The Modification of Diet in Renal Disease (MDRD) equation, for example, overestimates renal function among individuals with low muscle mass and underestimates it among those with GFR >60 ml/min per 1.73 m2.2–4 The use of serum cystatin C, a cysteine protease inhibitor that is freely filtered by the glomerulus, has potential advantages over creatinine as a filtration marker in that its production is not dependent on muscle mass.2 As a result, cystatin C offers opportunities to estimate GFR more accurately than creatinine-based equations and additionally may predict worsening kidney function even when the GFR is actually near the normal range.5 Beyond the relationship to measured GFR, cystatin-C–derived eGFR (ecGFR) was a better predictor of mortality than creatinine-based estimates in a study of elderly individuals6; however, the ability to generalize these findings to a younger and broader set of individuals is unknown. In this issue of JASN , Astor et al. 7 extend previous observations and demonstrate convincingly that ecGFR predicts mortality more accurately than the MDRD equation in a sample from the general population in the United States. If replicated, then these findings should spur trials to determine whether the use of cystatin C improves patient outcomes by identifying those with an elevated risk for death, both within and outside the setting of diagnosed chronic kidney disease (CKD). Astor et al. 7 focus on the relationship of ecGFR to mortality, but it is instructive to examine the …