title: Multicenter Evaluation of Cystatin C Measurement after Assay Standardization.
abstract: BACKGROUND
  Since 2010, a certified reference material ERM-DA471/IFCC has been available for cystatin C (CysC). This study aimed to assess the sources of uncertainty in results for clinical samples measured using standardized assays.
  
  
  METHODS
  This evaluation was performed in 2015 and involved 7 clinical laboratories located in France and Belgium. CysC was measured in a panel of 4 serum pools using 8 automated assays and a candidate isotope dilution mass spectrometry reference measurement procedure. Sources of uncertainty (imprecision and bias) were evaluated to calculate the relative expanded combined uncertainty for each CysC assay. Uncertainty was judged against the performance specifications derived from the biological variation model.
  
  
  RESULTS
  Only Siemens reagents on the Siemens systems and, to a lesser extent, DiaSys reagents on the Cobas system, provided results that met the minimum performance criterion calculated according to the intraindividual and interindividual biological variations. Although the imprecision was acceptable for almost all assays, an increase in the bias with concentration was observed for Gentian reagents, and unacceptably high biases were observed for Abbott and Roche reagents on their own systems.
  
  
  CONCLUSIONS
  This comprehensive picture of the market situation since the release of ERM-DA471/IFCC shows that bias remains the major component of the combined uncertainty because of possible problems associated with the implementation of traceability. Although some manufacturers have clearly improved their calibration protocols relative to ERM-DA471, most of them failed to meet the criteria for acceptable CysC measurements.
authors.affiliation: Laboratoire de Biochimie, CHRU de Montpellier, PhyMedExp, University of Montpellier, INSERM U1046, CNRS UMR 9214, Montpellier cedex 5, France.
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Bargnoux
authors.affiliation: Laboratoire de Biologie Médicale, Centre Hospitalier d'Avignon, Avignon, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Piéroni
authors.affiliation: Laboratoire de Biochimie, CHRU de Montpellier, PhyMedExp, University of Montpellier, INSERM U1046, CNRS UMR 9214, Montpellier cedex 5, France; jp-cristol@chu-montpellier.fr.
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Cristol
authors.affiliation: Laboratoire de Biochimie, CHRU de Montpellier, PhyMedExp, University of Montpellier, INSERM U1046, CNRS UMR 9214, Montpellier cedex 5, France.
authors.forename: Nils
authors.initials: N
authors.lastname: Kuster
authors.affiliation: Department of Nephrology, Dialysis and Hypertension, University of Liege, CHU Sart-Tilman, Liege, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Delanaye
authors.affiliation: Fédération de Biochimie, Centre Hospitalier Lyon Sud, Pierre Bénite, France.
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Carlier
authors.affiliation: Laboratoire de Biochimie et Hormonologie, Hôpital tenon, APHP, Paris, France.
authors.forename: Soraya
authors.initials: S
authors.lastname: Fellahi
authors.affiliation: Laboratoire de Biochimie Métabolique et Cellulaire, Hôpital Bichat-Claude Bernard, APHP, Paris, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Boutten
authors.affiliation: Laboratoire d'Immunochimie, Centre Hospitalier Lyon Sud, Pierre Bénite, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Lombard
authors.affiliation: Department of Physical and Analytical Chemistry, Faculty of Chemistry, University of Oviedo, Oviedo, Spain.|Department of Clinical Chemistry, University of Liege, CHU Sart-Tilman, Liege, Belgium.
authors.forename: Ana
authors.initials: A
authors.lastname: González-Antuña
authors.affiliation: Laboratoire National de Métrologie et d'Essais (LNE), Paris, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Delatour
authors.affiliation: Department of Clinical Chemistry, University of Liege, CHU Sart-Tilman, Liege, Belgium.
authors.forename: Etienne
authors.initials: E
authors.lastname: Cavalier
mesh_terms: D001331:Automation / Q000592:standards*; D001774:Blood Chemical Analysis / Q000592:standards*; D055316:Cystatin C / Q000097:blood* / Q000592:standards; D006801:Humans; D013058:Mass Spectrometry / Q000592:standards; D012015:Reference Standards
chemical_list: D055316:Cystatin C