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-triamine-penta-acetic acid) GFR (iGFR) was 88±2 ml 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.