Cystatin C - A Biomarker for Early Nephropathy in Type 2 Diabetic Patients

Diabetic nephropathy (DN) is a serious complication of diabetes associated with an increased risk of mortality, and cardiovascular and renal outcomes. Cystatin C, a 13 kD non-glycosylated basic protein, may be elevated in diabetic patients even before the appearance of microalbuminuria, and can be used as useful marker for detecting nephropathy in patients with normoalbuminuria (early nephropathy). We reviewed the recent literatures to determine if serum or urine cystatin C measurements could be useful as a marker to detect early DN in type 2 diabetic patients. Our search identified a total of 23 studies that have been published to date. Cystatin C measurement was carried out using immunoturbidimetric assays, Dade Behring Cystatin C assay, particle enhanced nephlometric immnuno assays, ELISA kits, or latex agglutination tests. Serum or urinary levels of cystatin C were elevated in type 2 diabetic patients compared to non-diabetic controls, including in patients who had no signs indicating nephropathy (without microalbuminuria). A significant positive correlation was found between cystatin C levels and albuminuria, suggesting its ability as a marker reflecting the degree of renal impairment in type 2 DN. Despite the promise of cystatin C as a biomarker, further large, multicenter prospective studies are still needed to confirm its clinical utility as a screening tool for early type 2 DN in every day practice.