Cystatin C- and Creatinine-Based Estimated Glomerular Filtration Rate, Vascular Disease, and Mortality in Persons With Diabetes in the U.S.

OBJECTIVE Serum cystatin C is an alternative to serum creatinine for estimating glomerular filtration rate (GFR), since cystatin C is less influenced by age and muscle mass. Among persons with diabetes, we compared the performance of GFR estimated using cystatin C (eGFR(cys)) with that using creatinine (eGFR(cr)) for the identification of reduced kidney function and its association with diabetes complications. RESEARCH DESIGN AND METHODS We analyzed data from adult participants from the 1999-2002 National Health and Nutrition Examination Survey with available cystatin C (N = 4,457). Kidney function was dichotomized as preserved (eGFR >= 60 mL/min/1.73 m(2)) or reduced (eGFR < 60 mL/min/1.73 m(2)) using the 2012 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) cystatin C and the 2009 CKD-EPI creatinine equations. RESULTS Among 778 persons with diabetes, the prevalence of reduced kidney function was 16.5% using eGFR(cr) and 22.0% using eGFR(cys). More persons with diabetes were reclassified from preserved kidney function by eGFR(cr) to reduced kidney function by eGFR(cys) than persons without diabetes (odds ratio 3.1 [95% CI 1.9-4.9], P < 0.001). The associations between lower eGFR and higher prevalence of albuminuria, retinopathy, peripheral arterial disease, and coronary artery disease were robust regardless of filtration marker. Similarly, the risk of all-cause mortality increased with lower eGFR(cr) and eGFR(cys). Only lower eGFR(cys) was significantly associated with cardiovascular mortality. CONCLUSIONS More persons with diabetes had reduced kidney function by eGFR(cys) than by eGFR(cr), and lower eGFR(cys) was strongly associated with diabetes complications. Whether eGFR(cys) is superior to eGFR(cr) in approximating true kidney function in a diabetic population requires additional study.