Estimating glomerular filtration rate in diabetes: a comparison of cystatin-C- and creatinine-based methods

Aims/hypothesis: We compared the predictive performance of a GFR based on serum cystatin C levels with commonly used creatinine-based methods in subjects with diabetes. Subjects, materials and methods: In a cross-sectional study of 251 consecutive clinic patients, the mean reference ( plasma clearance of 99mTc-diethylene-triaminepentaacetic acid) GFR (iGFR) was 88 +/- 2ml min(-1) 1.73 m(-2). A regression equation describing the relationship between iGFR and 1/cystatin C levels was derived from a test population (n=125) to allow for the estimation of GFR by cystatin C (eGFR-cystatin C). The predictive performance of eGFR-cystatin C, the Modification of Diet in Renal Disease 4 variable formula (MDRD-4) and Cockcroft-Gault (C-G) formulas were then compared in a validation population (n=126). Results: There was no difference in renal function (ml min(-1) 1.73 m(-2)) as measured by iGFR (89.2 +/- 3.0), eGFR-cystatin C ( 86.8 +/- 2.5), MDRD-4 (87.0 +/- 2.8) or C - G (92.3 +/- 3.5). All three estimates of renal function had similar precision and accuracy. Conclusions/interpretation: Estimates of GFR based solely on serum cystatin C levels had the same predictive potential when compared with the MDRD-4 and C - G formulas.