Serum cystatin C as an endogenous marker of renal function in patients with mild to moderate impairment of kidney function.

BACKGROUND: Estimation of the glomerular filtration rate (GFR) is essential for the evaluation of patients with chronic kidney disease (CKD). Recently, serum cystatin C was proposed as a new endogenous marker of GFR and in our study its diagnostic accuracy was compared with that of other markers of GFR. METHODS: In this study, 164 patients with CKD stages 2-3 (GFR 30-89 ml/min/1.73 m2), who had performed 51Cr-labelled ethylenediaminetetra-acetic acid clearance, were enrolled. In each patient, serum creatinine and serum cystatin C were determined. Creatinine clearance was calculated using the Cockcroft-Gault (C&G) and the modification of diet in renal disease (MDRD) formulas. RESULTS: The mean 51CrEDTA clearance was 57 ml/min/1.73 m2, the mean serum creatinine 149 micromol/l and the mean serum cystatin C 1.74 mg/l. We found significant correlation between 51CrEDTA clearance and serum creatinine (R = -0.666), serum cystatin C (R = -0.792), reciprocal of serum creatinine (R = 0.628), reciprocal of serum cystatin C (R = 0.753) and calculated creatinine clearance from the formulas C&G (R = 0.515) and MDRD formulas (R = 0.716). The receiver operating characteristic (ROC) curve analysis (cut-off for GFR 60 ml/min/1.73 m2) showed that serum cystatin C had a significantly higher diagnostic accuracy than serum creatinine (P = 0.04) and calculated creatinine clearance from the C&G formula (P < 0.0001), though only in female patients. No difference in diagnostic accuracy was found between serum cystatin C and creatinine clearance calculated from the MDRD formula. CONCLUSIONS: Our results indicate that serum cystatin C is a reliable marker of GFR in patients with mildly to moderately impaired kidney function and has a higher diagnostic accuracy than serum creatinine and calculated creatinine clearance from the C&G formula in female patients.