Cystatin C, renal function, and cardiovascular risk.

Because all the patients had chronic kidney disease (CKD) (GFR <55 mL/min per 1.73 m 2 ), this study cannot be used to assert that cystatin C is definitively better than creatinine for detecting stage 3 kidney disease (GFR <60 mL/min per 1.73 m 2 ). Regarding the study methods, the authors do not mention when cystatin C was measured in the frozen samples. Were the samples measured retrospectively? If so, are the authors sure of the stability of the cystatin C in samples frozen, for example, for more than 10 years? The authors found that cystatin C is associated with body mass index. This interesting result should be discussed in light of the recent literature (2). The authors compared cystatin C with estimated GFR to predict cardiovascular risk. Why have they not studied an equation based on cystatin C, such as the one published by Rule and colleagues (3)?