title: Application of the characteristic function to evaluate and compare analytical variability in an external quality assessment scheme for serum ethanol.
abstract: BACKGROUND
  As a cornerstone of quality management in the laboratory, External Quality Assessment (EQA) schemes are used to assess laboratory and analytical method performance. The characteristic function is used to describe the relation between the target concentration and the EQA standard deviation, which is an essential part of the evaluation process. The characteristic function is also used to compare the variability of different analytical methods.
  
  
  METHODS
  We fitted the characteristic function to data from the Belgian External Quality Assessment program for serum ethanol. Data included results from headspace gas chromatography and the enzymatic methods of Abbott, Roche, Siemens, and Ortho-Clinical Diagnostics. We estimated the characteristic function with weighted nonlinear regression. By introducing dummy variables, we rewrote the original formula of the characteristic function to assess statistical inference for comparing the variability of the different analytical methods.
  
  
  RESULTS
  The characteristic function fitted the data precisely. Comparison between methods showed that there was little difference between the estimated variability for low concentrations, and that the increase in SD with increasing target concentration was slower for Abbott and Roche than for the other methods.
  
  
  CONCLUSIONS
  The characteristic function can successfully be introduced in clinical schemes, although its applicability to fit the data should always be assessed. Because of its easy parameterization, it can be used to assess differences in performance between analytical methods and to assess laboratory performance. The characteristic function also offers an alternative framework for coefficients of variation to describe variability of analytical methods.
authors.affiliation: Quality of Medical Laboratories, Scientific Institute of Public Health, Brussels, Belgium; wim.coucke@wiv-isp.be.
authors.forename: Wim
authors.initials: W
authors.lastname: Coucke
authors.affiliation: Department of Toxicology, University Hospital of Liège, Liège, Belgium;
authors.forename: Corine
authors.initials: C
authors.lastname: Charlier
authors.affiliation: Laboratory of Toxicology, Ghent University, Ghent, Belgium;
authors.forename: Willy
authors.initials: W
authors.lastname: Lambert
authors.affiliation: Department of Clinical Chemistry, AZ Groeninge Hospital, Kortrijk, Belgium;
authors.forename: Frank
authors.initials: F
authors.lastname: Martens
authors.affiliation: Laboratory of Toxicology, ZNA Stuivenberg, Antwerp, Belgium; Toxicological Center, University of Antwerp, Antwerp, Belgium;
authors.forename: Hugo
authors.initials: H
authors.lastname: Neels
authors.affiliation: Laboratory of Toxicology and Pharmacology, Katholieke Universiteit Leuven, Leuven, Belgium;
authors.forename: Jan
authors.initials: J
authors.lastname: Tytgat
authors.affiliation: Quality of Medical Laboratories, Scientific Institute of Public Health, Brussels, Belgium;
authors.forename: Philippe
authors.initials: P
authors.lastname: Van de Walle
authors.affiliation: Gamma Medic SPRL, Isnes, Belgium;
authors.forename: André
authors.initials: A
authors.lastname: Vanescote
authors.affiliation: Louvain Centre for Toxicology and Applied Pharmacology, Université Catholique de Louvain, Brussels, Belgium;
authors.forename: Pierre
authors.initials: P
authors.lastname: Wallemacq
authors.affiliation: Toxicology Department, Federal Public Service Justice, National Institute of Criminalistics and Criminology, Brussels, Belgium;
authors.forename: Sarah
authors.initials: S
authors.lastname: Wille
authors.affiliation: Department of Laboratory Medicine, Ghent University, Ghent, Belgium; Department of Clinical Chemistry, Microbiology, and Immunology, Ghent University, Ghent, Belgium.
authors.forename: Alain G
authors.initials: AG
authors.lastname: Verstraete
mesh_terms: D001774:Blood Chemical Analysis / Q000379:methods* / Q000592:standards*; D002849:Chromatography, Gas / Q000592:standards; D000431:Ethanol / Q000097:blood*; D006801:Humans; D007753:Laboratories / Q000592:standards; D011786:Quality Control; D012044:Regression Analysis
chemical_list: D000431:Ethanol