A Comparison of Estimated GFRs Based on Formulas of Serum Cystatin C and Serum Creatinine

Background Serum cystatin C has been identified as a marker for the estimation of glomerular filtration rate (GFR). Although this marker is more sensitive than creatinine, it is too expensive and not available in all laboratories. In this study, we compared cystatin C-based equations with creatinine-based formulas to select the most precise creatinine-based formula for estimating GFR in patients with chronic kidney disease (CKD). Methods 120 patients with CKD were enrolled in this cross-sectional study. The patients were divided into groups according to BMI (< 25, 25 - 29.9, and ≥ 30) and age (≤ 40, 41 - 60, and ≥ 60). The patients’ GFRs were estimated and analyzed by using three creatinine-based equations (modification of diet in renal disease (MDRD), abbreviated MDRD, and Cockcroft and Gault (C-G)) and five cystatin C-based equations (Filler, Le Bricon, Rule, Hoek, and Larsson). Results The mean age of patients was 56.4 ± 16.4 years. The mean of GFRs using C-G, MDRD, and abbreviated MDRD formulas were 36.2 ± 14.3, 32.6 ± 11.4, and 32.4 ± 11.3 mL/min/1.73 m², respectively. The mean of GFRs using Filler, Le Bricon, Larsson, Rule, and Hoek equations were 54.7 ± 20.1, 53.0 ± 15.7, 43.6 ± 18.5, 45.1 ± 17.2, and 46.2 ± 16.2 mL/min/1.73 m², respectively. The closest correlation was observed between GFRs generated by Abbreviated MDRD and cystatin C-based equations (P < 0.001, r: 0.4, R²: 0.16). Differences in GFR estimation between cystatin C-based equations and C-G equation were lower at higher BMI levels (P: 0.004 - 0.01, F: 4.5 - 6.7). Differences in GFR estimation between cystatin C-based equations and C-G as well as MDRD equations were greater in older patients (P: 0.01 - 0.04, F: 3.2 - 4.1). Conclusions GFRs estimated by Abbreviated MDRD equation are closer to GFRs estimated by cystatin C equations regardless of patients’ BMI in CKD subjects.