Cystatin C and Cystatin Glomerular Filtration Rate as Markers of Early Renal Disease in Asian Indian Subjects With Glucose Intolerance (CURES-32)

BACKGROUND: The aim of this study was to assess cystatin C (cys-C) as a marker of early diabetic nephropathy and cystatin glomerular filtration rate (cys-GFR) in Asian Indians. METHODS: Five groups of subjects were studied: Group 1, normal glucose tolerance (NGT) and normoalbuminuria (n = 43); group 2, impaired glucose tolerance (IGT) and normoalbuminuria (n = 44); group 3, type 2 diabetes (T2DM) with neither microalbuminuria nor retinopathy (n = 40); group 4, T2DM with microalbuminuria but without diabetic retinopathy (n = 40); and group 5, T2DM with microalbuminuria and any degree of diabetic retinopathy (DR) (n = 42). Subjects were recruited from the Chennai Urban Rural Epidemiology Study (CURES). Microalbumin concentration was assessed in the urine sample by immunoturbidometric assay. cys-C concentrations were measured in serum by a high-sensitivity particle-enhancing nephlometric assay. cys-GFR was calculated by the formula (86.7/cys-C) - 4.2. RESULTS: cys-C levels were highest in group 5 (1.75 +/- 0.12 mg/L) followed by group 4 (1.30 +/- 0.08 mg/L), group 3 (0.98 +/- 0.04 mg/L), group 2 (0.89 +/- 0.03 mg/L), and group 1 (0.79 +/- 0.18 mg/L, P < 0.001). cys-GFR levels were in reverse order going from highest in group 1, followed by groups 2, 3, 4, and 5. cys-C levels were correlated with age, fasting plasma glucose, glycosylated hemoglobin, microalbuminuria, and serum cholesterol. CONCLUSIONS: cys-C levels increase and cys-GFR levels decrease with increasing severity of glucose intolerance and are highest and lowest, respectively, in type 2 diabetes mellitus (T2DM) subjects with microalbuminuria and retinopathy. In T2DM subjects, cys-C and cys-GFR appear to be useful markers of early renal damage.