Evaluation of glomerular filtration rate using cystatin C in diabetic patients analysed by multiple factors including tubular function.

This study was designed to evaluate the usefulness of serum cystatin C (CysC) as a marker of renal function in 83 patients with diabetic nephropathy, considering multiple factors including tubular function and body mass index. Serum CysC was assayed using a particle-enhanced nephelometric immunoassay and the glomerular filtration rate (GFR) was obtained by measuring the plasma disappearance of the isotope Tc-99m-diethylenetriamine penta-acetic acid. By comparing the correlation of CysC and serum creatinine (SCr) with GFR, it was concluded that CysC may be a better indicator of GFR than SCr in diabetic patients, in both the early hypertransfusion stage and in the late renal dysfunction stage. CysC showed a slightly higher sensitivity for renal function evaluation than SCr in patients with renal tubular dysfunction and moderate to severe proteinuria. In addition, CysC was not affected by the metabolic index. Thus, CysC may serve as an ideal endogenous marker of GFR in patients with diabetic nephropathy.