title: Proposal of a candidate international conventional reference measurement procedure for free thyroxine in serum.
abstract: In the present paper the IFCC WG-STFT recommends and provides the rationale to establish metrological traceability of serum free thyroxine (FT4) measurements to a candidate international conventional reference measurement procedure. It is proposed that this procedure be based on equilibrium dialysis combined with determination of thyroxine in the dialysate with a trueness-based reference measurement procedure. The measurand is thus operationally defined as "thyroxine in the dialysate from equilibrium dialysis of serum prepared under defined conditions". With regard to the trueness-based reference measurement procedure, the WG-STFT recommends use of an isotope dilution-liquid chromatography/tandem mass spectrometry (ID-LC/tandem MS) procedure for total thyroxine that has been optimized towards measurement at picomolar concentration levels and that is listed in the database of the Joint Committee for Traceability in Laboratory Medicine (JCTLM). For calibration, the purified thyroxine material IRMM-468 (resulting from a project funded by the European Commission and recently submitted to the JCTLM) is proposed. The WG-STFT stresses that according to this recommendation it is a prerequisite to strictly adhere to the defined equilibrium dialysis procedure, whereas it is permissible to introduce variants in the ID-LC/tandem MS procedure.
authors.affiliation: Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium. linda.thienpont@ugent.be
authors.forename: Linda M
authors.initials: LM
authors.lastname: Thienpont
authors.forename: Graham
authors.initials: G
authors.lastname: Beastall
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Christofides
authors.forename: James D
authors.initials: JD
authors.lastname: Faix
authors.forename: Tamio
authors.initials: T
authors.lastname: Ieiri
authors.forename: Véronique
authors.initials: V
authors.lastname: Jarrige
authors.forename: W Greg
authors.initials: WG
authors.lastname: Miller
authors.forename: Richard
authors.initials: R
authors.lastname: Miller
authors.forename: Jerald C
authors.initials: JC
authors.lastname: Nelson
authors.forename: Cathérine
authors.initials: C
authors.lastname: Ronin
authors.forename: H Alec
authors.initials: HA
authors.lastname: Ross
authors.forename: Michael
authors.initials: M
authors.lastname: Rottmann
authors.forename: Jos H
authors.initials: JH
authors.lastname: Thijssen
authors.forename: Brigitte
authors.initials: B
authors.lastname: Toussaint
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods*; D003956:Dialysis / Q000379:methods; D006801:Humans; D007554:Isotopes; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry / Q000379:methods*; D013974:Thyroxine / Q000097:blood*; D014462:Ultrafiltration / Q000379:methods
chemical_list: D007554:Isotopes; D013974:Thyroxine