Background. The aim of this study was to compare two methods used to measure serum cystatin C (Cys), and their accuracy to predict glomerular filtration rate (GFR).

Patients and Methods. Three hundred-sixty seven adult chronic kidney disease (CKD) patients with different functional impairment participated to this study. GFR was determined as the renal clearance of 99mTc-DTPA. Serum concentrations of cystatin C (SCys) were determined with an immunonephelometric method and with an immunoturbidimetric method.

Results. A very high linear correlation was found between the two measurements of SCys (r=0.929). The mean difference SCysTurb-SCysNeph was 0.02±0.43 mg/L (NS). A high logarithmic correlation was also found between SCys and GFR (r was 0.919 for SCysNeph and 0.937 for SCysTurb). By means of multiple regression analysis, we developed formulas to predict GFR from SCysNeph, SCysTurb, and SCr. For comparison, GFR was predicted using published formulas. A good agreement was found between predicted GFR and measured GFR. The accuracy of SCysNeph, SCysTurb and SCreat, and of the different prediction formulas resulted quite similar.

Conclusion. The immunoturbidimetric method seems adequate to measure SCys and to predict GFR and its impairment in CKD, at least like the immunonephelometric method. The accuracy of SCys and of derived formulas was not higher than that of SCr and SCr-based formulas.