Estimation of Glomerular Filtration Rate Based on Serum Cystatin C versus Creatinine in a Uruguayan Population

Background. Estimation of glomerular filtration rate (eGFR) from biomarkers has evolved and multiple equations are available to estimate renal function at bedside. Methods. In a random sample of 119 Uruguayans (54.5% women; 56.2 years (mean)), we used Bland and Altman's method and Cohen's kappa statistic to assess concordance on a continuous or categorical (eGFR < 60 versus ≥60 mL/min/1.73 m(2)) scale between eGFR(cys) (reference) and eGFR derived from serum creatinine according to the Modification of Diet in Renal Disease (eGFR(mdrd)) or the Chronic Kidney Disease Epidemiology Collaboration equations (eGFR(epi)) or from both serum cystatin C and creatinine (eGFR(mix)). Results. In all participants, eGFR(mdrd), eGFR(epi), and eGFR(mix) were, respectively, 9.7, 11.5, and 5.6 mL/min/1.73 m(2) higher (P < 0.0001) than eGFR(cys). The prevalence of eGFR <60 mL/min/1.73 m(2) was the highest for eGFR(cys) (21.8%), intermediate for eGFR(mix) (11.8%), and the lowest for eGFR(mdrd) (5.9%) and eGFR(epi) (3.4%). Using eGFR(cys) as reference, we found only fair agreement with the equations based on creatinine (Cohen's kappa statistic 0.15 to 0.23). Conclusion. Using different equations we reached clinically significant differences in the estimation of renal function. eGFR(cys) provides lower estimates, resulting in higher prevalence of eGFR <60 mL/min/1.73 m(2).