Serum cystatin C measured by a sol particle homogeneous immunoassay can accurately detect early impairment of renal function

Background A sol particle homogeneous immunoassay (SPIA) is a method to measure the serum cystatin C (cysC) level as a marker of the glomerular filtration rate (GFR). Recently, formulas to convert measured cysC to GFR have been developed. Methods A total of 154 patients (46 +/- 18 years old) who had undergone renal biopsy, sodium thiosulfate clearance (C-thio) and 24-h creatinine clearance (24-hCcr) tests were subjects for the study. Their serum cysC levels were determined by SPIA. Results Multiple regression analysis revealed Cthio and age as independent variables for serum creatinine concentration (Cr), while only C-thio affected cysC. The equations using Cr or cysC showed significant correlation with C-thio. Receiver-operating curve ROC analysis revealed that cysC and 24-hCcr shared comparable power to detect patients with GFR < 90 or 60 ml/min/1.73 m(2) (AUC = 0.862 and 0.943 vs. AUC = 0.842 and 0.943, respectively), while Cr (AUC = 0.881) and MDRD2 (AUC = 0.888) showed slightly inferior ability to detect 60 ml/min/1.73 m(2) than other parameters in the female population. The cut-off point of cysC and Cr obtained from the ROC analysis demonstrated strong power to detect patients with C-thio < 90ml/min/1.73 m(2) or C-thio < 60 ml/min/1.73 m(2). According to CKD stages, the mean values of each equation were significantly different, like that demonstrated by 24-hCcr. Conclusion SPIA could determine cysC levels that detected early renal impairment. The accuracy of cysC to detect early renal impairment may be superior to that of Cr in females, while it would be comparable to that of CG or MDRD when they are corrected by sex and age. Both cysC itself and cysC equations are effective to monitor the progress of renal impairment. The future standardization of cysC measurements and development of novel equation of cysC would contribute to the further improvement of GFR estimation in clinical practice.