Serum cystatin C as a marker for early detection of chronic kidney disease and grade 2 nephropathy in Japanese patients with type 2 diabetes

Background: Diabetic nephropathy (DN) is a significant cause of hemodialysis, and its early detection is extremely important to prevent or delay end-stage renal disease. The significance of the renal function marker serum cystatin C (sCysC) and its relationship with glomerular filtration rate in chronic kidney disease (CKD) and DN in Japanese patients with type 2 diabetes remains uncertain. In this study, we examined the effectiveness of sCysC as a marker of early DN and CKD in Japanese subjects. Methods: A total of 325 Japanese patients with type 2 diabetes and 88 healthy subjects were studied retrospectively. sCysC concentration (mg/L) was determined by a latex turbidmetric immunoassay using a BioMajesty 8040 analyzer. The renal function of the diabetic patients was evaluated using the albumin-creatinine ratio (ACR) and Kidney Disease Outcome Quality Initiative-Kidney Disease Improving Global Outcomes (K/DOQI-KDIGO) classification. Results: There was a significant increase in sCysC but not in serum creatinine (sCr) or serum beta(2)-microglobulin (s beta 2M) in patients with grade 2 DN (ACR 30-300 mg/g) compared to grade 1 patients. Receiver operating characteristic analysis in grade 2 and 3 DN patients showed that sCysC had superior sensitivity and specificity than sCr and s beta 2M for early detection of DN. In addition, sCysC showed particularly high sensitivity and specificity in DN patients with stage 2 CKD. Conclusions: sCysC was effective for detection of grade 2 DN and would be especially useful for screening stage 2 CKD patients (K/DOQI-KDIGO).