title: A multicenter comparison of whole blood vitamin B6 assays.
abstract: BACKGROUND
  The aim of this study was to compare different analytical methods that are currently in use in the Netherlands for the measurement of whole blood vitamin B6.
  
  
  METHODS
  This method comparison study consisted of two separate parts. (1) Four laboratories participated in a pilot study in which the commercial Chromsystems and INstruchemie method, and a laboratory developed liquid chromatography-tandem mass spectrometry (LC-MS/MS) method and HPLC method were compared. Sixty-nine frozen whole blood samples and six lyophilized whole blood samples were used for comparison. (2) In the nationwide part of the study, 49 laboratories participated in the analysis of three identical sets of two whole blood samples of which one set was freshly analyzed, one set was analyzed after storage at -20 °C and one set was analyzed after lyophilization.
  
  
  RESULTS
  In both parts of the study, the HPLC and LC-MS/MS methods showed equivalent results for all sample types tested. The Chromsystems method showed a positive bias of 45% (pilot study) and 30% (nationwide study) towards the LC-MS/MS method when fresh or frozen samples were used. The measurement of lyophilized samples showed no differences between the methods. The results of the INstruchemie method were inconclusive due to the low number of participants.
  
  
  CONCLUSIONS
  The different analytical methods for measuring vitamin B6 produce different results when whole blood patient samples are measured. The recognition of a reference method or the development of suitable reference materials and quality control materials might serve as a first step towards improved standardization or harmonization of the whole blood vitamin B6 assay.
authors.forename: Bertrand D
authors.initials: BD
authors.lastname: van Zelst
authors.forename: Roseri J A C Roelofsen
authors.initials: RJ
authors.lastname: de Beer
authors.forename: Marjolein
authors.initials: M
authors.lastname: Neele
authors.forename: Snježana
authors.initials: S
authors.lastname: Kos
authors.forename: Ido P
authors.initials: IP
authors.lastname: Kema
authors.forename: Frans P W
authors.initials: FP
authors.lastname: Tegelaers
authors.forename: Christa M
authors.initials: CM
authors.lastname: Cobbaert
authors.forename: Cas W
authors.initials: CW
authors.lastname: Weykamp
authors.forename: Robert
authors.initials: R
authors.lastname: de Jonge
mesh_terms: D001774:Blood Chemical Analysis; D002853:Chromatography, Liquid; D019411:Clinical Laboratory Techniques; D006801:Humans; D015337:Multicenter Studies as Topic; D010865:Pilot Projects; D053719:Tandem Mass Spectrometry; D025101:Vitamin B 6 / Q000097:blood*
chemical_list: D025101:Vitamin B 6