title: Analytical performances of cystatin C turbidimetric assay: which impact on accuracy of glomerular filtration rate estimation in renal transplantation?
abstract: BACKGROUND
  The potential use of cystatin C has recently emerged to evaluate kidney function following transplantation. Analytical performance of a particle-enhanced turbidimetric immunoassay (PETIA) using Dako Cytomation Cystatin C reagents on an Olympus AU640(®) analyzer was evaluated. Clinical relevance was determined by comparison with a reference method in a kidney transplant cohort.
  
  
  METHODS
  Repeatability and reproducibility were carried out for four levels of cystatin C. Linearity was done by successive dilution of plasma samples with high level of cystatin C. Comparison study was performed against the particle-enhanced nephelemetry immunoassay (PENIA) using Siemens reagents on BNII(®) system. Values of the glomerular filtration rate (GFR) estimated from several predictive cystatin C- and creatinine-based equations were compared to the GFR measured by isotopic method ((99m)Tc-DTPA). These predictive algorithms were analyzed with respect to bias, precision and accuracy.
  
  
  RESULTS
  Total intra-assay and inter-assay variation coefficients were below 4% at the four levels tested. Values obtained with Dako-PETIA on AU640(®) were correlated with the Siemens-PENIA method (Dako-Olympus=0.88 Siemens+0.17). The cystatin C alone and the creatinine-cystatin C combined equation allowed reliable assessment of GFR in our population of renal transplants. The cystatin C-based or the combined equation moderately improved determination of GFR (about 10% compared to 175MDRD for classification into the correct K/DOQI CKD stages).
  
  
  CONCLUSIONS
  The use of algorithms based on cystatin C and creatinine could provide a reliable estimate of the GFR in kidney transplantation. Standardization of cystatin C assays could further improve the predicting value of cystatin C in transplantation.
authors.affiliation: Department of Biochemistry, University of Montpellier, University Hospital of Montpellier, France.
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Bargnoux
authors.forename: Marie
authors.initials: M
authors.lastname: Perrin
authors.forename: Valérie
authors.initials: V
authors.lastname: Garrigue
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Badiou
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Dupuy
authors.forename: Georges
authors.initials: G
authors.lastname: Mourad
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Cristol
mesh_terms: D000465:Algorithms; D019963:Clinical Chemistry Tests / Q000592:standards*; D055316:Cystatin C / Q000652:urine*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D016030:Kidney Transplantation; D008297:Male; D015203:Reproducibility of Results
chemical_list: D055316:Cystatin C