title: Systematic monitoring of standardization and harmonization status with commutable EQA-samples--five year experience from the Netherlands.
abstract: BACKGROUND
  Equivalence of results among laboratories is a major mission for medical laboratories. Monitoring of test equivalence is structurally integrated in the Dutch External Quality Assessment (EQA) scheme since 2005. Commutable poolsera, single donation "spy" sera and biological variance tolerance limits have been introduced in the EQA scheme for evaluation of the degree of test equivalence and its determinants.
  
  
  METHODS
  In the annual cycle scheme 24 samples, covering the (patho)physiological measuring range for 17 analytes, are assayed by 220 participating laboratories at biweekly intervals. Test equivalence was evaluated by calculating overall median interlaboratory coefficients of variation (CVs) and its bias and imprecision components. Data from 2005 and 2010 schemes are evaluated to investigate trends in performance and success of standardization efforts.
  
  
  RESULTS
  Overall median interlaboratory CVs in 2010 were mostly better than in 2005. Median interlaboratory CVs became <5% for electrolytes and substrates, and <10% for enzymes. Improvement in median interlaboratory CVs over these five years is mainly explained by improved method standardization, especially for enzymes and creatinine.
  
  
  CONCLUSIONS
  The Dutch EQA-program proves to be a powerful instrument to evaluate test equivalence. It allows monitoring standardization efforts in a highly effective way and gives insight into remaining standardization potential.
authors.affiliation: Leiden University Medical Center, Leiden, The Netherlands. c.m.cobbaert@lumc.nl
authors.forename: Christa
authors.initials: C
authors.lastname: Cobbaert
authors.forename: Cas
authors.initials: C
authors.lastname: Weykamp
authors.forename: Paul
authors.initials: P
authors.lastname: Franck
authors.forename: Robert
authors.initials: R
authors.lastname: de Jonge
authors.forename: Aldy
authors.initials: A
authors.lastname: Kuypers
authors.forename: Herman
authors.initials: H
authors.lastname: Steigstra
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Klein Gunnewiek
authors.forename: Douwe
authors.initials: D
authors.lastname: van Loon
authors.forename: Rob
authors.initials: R
authors.lastname: Jansen
mesh_terms: D001774:Blood Chemical Analysis; D003404:Creatinine / Q000097:blood; D004573:Electrolytes / Q000097:blood; D004798:Enzymes / Q000097:blood / Q000378:metabolism; D006801:Humans; D009426:Netherlands; D011785:Quality Assurance, Health Care / Q000592:standards*; D012016:Reference Values
chemical_list: D004573:Electrolytes; D004798:Enzymes; D003404:Creatinine