title: Performance in Measurement of Serum Cystatin C by Laboratories Participating in the College of American Pathologists 2014 CYS Survey.
abstract: BACKGROUND
  Cystatin C is becoming an increasingly popular biomarker for estimating glomerular filtration rate, and accurate measurements of cystatin C concentrations are necessary for accurate estimates of glomerular filtration rate.
  
  
  OBJECTIVE
  To assess the accuracy of cystatin C concentration measurements in laboratories participating in the College of American Pathologists CYS Survey.
  
  
  METHODS
  Two fresh frozen serum pools, the first from apparently healthy donors and the second from patients with chronic kidney disease, were prepared and distributed to laboratories participating in the CYS Survey along with the 2 usual processed human plasma samples. Target values were established for each pool by using 2 immunoassays and ERM DA471/IFCC international reference material.
  
  
  RESULTS
  For the normal fresh frozen pool (ERM-DA471/IFCC-traceable target of 0.960 mg/L), the all-method mean (SD, % coefficient of variation [CV]) reported by all of the 123 reporting laboratories was 0.894 mg/L (0.128 mg/L, 14.3%). For the chronic kidney disease pool (ERM-DA471/IFCC-traceable target of 2.37 mg/L), the all-method mean (SD, %CV) was 2.258 mg/L (0.288 mg/L, 12.8%). There were substantial method-specific biases (mean milligram per liter reported for the normal pool was 0.780 for Siemens, 0.870 for Gentian, 0.967 for Roche, 1.061 for Diazyme, and 0.970 for other/not specified reagents; and mean milligram per liter reported for the chronic kidney disease pool was 2.052 for Siemens, 2.312 for Gentian, 2.247 for Roche, 2.909 for Diazyme, and 2.413 for other/not specified reagents).
  
  
  CONCLUSIONS
  Manufacturers need to improve the accuracy of cystatin C measurement procedures if cystatin C is to achieve its full potential as a biomarker for estimating glomerular filtration rate.
authors.forename: John H
authors.initials: JH
authors.lastname: Eckfeldt
authors.forename: Amy B
authors.initials: AB
authors.lastname: Karger
authors.forename: W Greg
authors.initials: WG
authors.lastname: Miller
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Rynders
authors.affiliation: From the Department of Laboratory Medicine and Pathology (Drs Eckfeldt and Karger).|and the Advanced Research and Diagnostic Laboratory (Mr Rynders).|University of Minnesota, Minneapolis; the Department of Pathology, Virginia Commonwealth University, Richmond (Dr Miller);|and the Division of Nephrology, Tufts Medical Center, Boston, Massachusetts (Dr Inker).
authors.forename: Lesley A
authors.initials: LA
authors.lastname: Inker
mesh_terms: D055316:Cystatin C / Q000097:blood*; D005919:Glomerular Filtration Rate; D019538:Health Care Surveys; D006801:Humans; D007677:Kidney Function Tests; D007753:Laboratories / Q000592:standards*; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000175:diagnosis*; D014481:United States
chemical_list: D055316:Cystatin C