Cystatin C is a reliable marker for estimation of glomerular filtration rate in renal transplantation: validation of a new turbidimetric assay using monospecific sheep antibodies

Background: The potential use of cystatin C was recently assessed in kidney transplantation. A new particle-enhanced turbidimetric immunoassay (PETIA) that uses sheep antibodies (Binding Site human cystatin C immunoassay) has been developed. Analytical performance of this new assay was evaluated. Clinical relevance was determined by comparison with a reference method in a cohort of kidney transplant patients. Methods: First, the analytical performance of the Binding Site cystatin C kit was tested on SPA(PLUS)(R) and Hitachi (R) analyzers. Second, a comparison study was performed using SPA(PLUS)(R) analyzer against two other cystatin C methods (the Siemens-PENIA method on BNII (R) and the Dako-PETIA application on Olympus AU640 (R)). Third, the glomerular filtration rate (GFR) was estimated using several predictive cystatin C- and creatinine-based equations and compared to GFR measured by an isotopic method (Tc-99m-DTPA). These predictive algorithms were analyzed with respect to bias, precision and accuracy. Results: Total intra-assay and inter-assay coefficients of variation were below 5%. Values obtained with the SPA(PLUS)(R) correlated with the Siemens-PENIA and the Dako-PETIA methods. The creatinine and cystatin C-based equation allowed reliable assessment of GFR in our population of renal transplantation. Conclusions: The use of algorithms based on cystatin C and creatinine could provide a reliable estimate of GFR in kidney transplantation.