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Clinical Chemistry and Laboratory Medicine (CCLM)

Published in Association with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)

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Proposal of a candidate international conventional reference measurement procedure for free thyroxine in serum

International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), IFCC Scientific Division: Working Group for Standardization of Thyroid Function Tests (WG-STFT): Linda M. Thienpont1 / Graham Beastall2 / Nicholas D. Christofides3 / James D. Faix4 / Tamio Ieiri5 / Véronique Jarrige6 / W. Greg Miller7 / Richard Miller8 / Jerald C. Nelson9 / Cathérine Ronin10 / H. Alec Ross11 / Michael Rottmann12 / Jos H. Thijssen13 / Brigitte Toussaint14

1Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium

2Department of Clinical Biochemistry, Royal Infirmary, Glasgow, UK

3Research and Development, Ortho-Clinical Diagnostics, Cardiff Laboratories, Whitchurch, UK

4Stanford Medical School, Palo Alto, CA, USA

5Department of Clinical Laboratory Medicine, Dokkyo University School of Medicine, Japan

6Beckman Coulter Eurocenter, Nyon, Switzerland

7Department of Pathology, Virginia Commonwealth University, Richmond, VA, USA

8Dade Behring Inc., Newark, DE, USA

9Department of Medicine, Loma Linda University School of Medicine, Loma Linda, CA 92354, USA

10Laboratoire de Neurobiologie, Centre National de la Recherche Scientifique, Marseille, France

11Department of Chemical Endocrinology, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands

12Roche Diagnostics GmbH, Penzberg, Germany

13Laboratory of Endocrinology, University Medical Center Utrecht, Utrecht, The Netherlands

14Institute for Reference Materials and Measurements (IRMM), Joint Research Center, European Commission, Geel, Belgium

Corresponding author: Prof. Linda Thienpont, Laboratory for Analytical Chemistry, Ghent University, Harelbekestraat 72, 9000 Ghent, Belgium Phone +32-9-264 81 04, Fax +32-9-264 81 98,

Citation Information: Clinical Chemical Laboratory Medicine. Volume 45, Issue 7, Pages 934–936, ISSN (Online) 14374331, ISSN (Print) 14346621, DOI: 10.1515/CCLM.2007.155, July 2007

Publication History

Published Online:


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.

Clin Chem Lab Med 2007;45:934–6.

Keywords: equilibrium dialysis; free thyroxine; international conventional reference measurement procedure; isotope dilution-liquid chromatography-tandem mass spectrometry; metrological traceability; serum

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