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Clinical Chemistry 51: 161-168, 2005. First published November 18, 2004; 10.1373/clinchem.2004.041772
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(Clinical Chemistry. 2005;51:161-168.)
© 2005 American Association for Clinical Chemistry, Inc.

Endocrinology and Metabolism

Metrologic Traceability of Total Thyroxine Measurements in Human Serum: Efforts to Establish a Network of Reference Measurement Laboratories

Linda M. Thienpont1,a, Katleen Van Uytfanghe1, John Marriot2, Peter Stokes2, Lothar Siekmann3, Anja Kessler3, David Bunk4 and Susan Tai4

1 Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Gent, Belgium.
2 Laboratory of the Government Chemist, Teddington, United Kingdom.
3 Institute for Clinical Biochemistry, University of Bonn, Bonn, Germany.
4 National Institute of Standards and Technology, Gaithersburg, MD.

aAddress correspondence to this author at: Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Harelbekestraat 72, 9000 Gent, Belgium. Fax 32-9-264-8198; e-mail linda.thienpont{at}ugent.be.

Background: Assuring/demonstrating metrologic traceability of in vitro diagnostics necessitates the availability of measurand-specific reference measurement systems (RMSs) and the possibility for industry to work with competent reference measurement laboratories (RMLs). Here we report the results of a European project to investigate the feasibility of developing a RMS for serum total thyroxine.

Methods: Four candidate RMLs (cRMLs) developed/implemented variants of a candidate reference measurement procedure (cRMP) based on isotope dilution–liquid chromatography–mass spectrometry. The sole constraint implemented was calibration with a common thyroxine primary calibrator. The RMPs were externally validated and assessed for comparability in round-robin trials using common samples, i.e., 5 lyophilized and 33 frozen native sera. At the same time, the performance of the cRMLs organized in a network was assessed. For uniform external quality assessment, common performance specifications were agreed on.

Results: All cRMLs performed the cRMPs with fulfillment of the predefined specifications: total and between-laboratory CVs ≤2.0% and 2.5%, respectively, and a systematic deviation ≤0.9%, estimated with a target assigned from the mean of means obtained by the cRMLs. The mean expanded uncertainty for value assignment to the native sera was 2.1%.

Conclusions: A network of cRMLs, with externally conformed competence to properly perform RMPs, has been established. Performance specifications were defined and will form the basis for admittance of new network members. A serum panel, successfully targeted during the validation process, is available for split-sample measurements with commercial routine measurement procedures. The model can now be used for other measurands for which traceability to the Système International d’Unités is needed.




The following articles in journals at HighWire Press have cited this article:


Home page
 Clin. Chem.Home page
K. Van Uytfanghe, D. Stockl, H A. Ross, and L. M. Thienpont
Use of Frozen Sera for FT4 Standardization: Investigation by Equilibrium Dialysis Combined with Isotope Dilution-Mass Spectrometry and Immunoassay
Clin. Chem., September 1, 2006; 52(9): 1817 - 1821.
[Abstract] [Full Text] [PDF]

Home page
 Clin. Chem.Home page
L. M. Thienpont, K. Van Uytfanghe, J. Marriott, P. Stokes, L. Siekmann, A. Kessler, D. Bunk, and S. Tai
Feasibility Study of the Use of Frozen Human Sera in Split-Sample Comparison of Immunoassays with Candidate Reference Measurement Procedures for Total Thyroxine and Total Triiodothyronine Measurements
Clin. Chem., December 1, 2005; 51(12): 2303 - 2311.
[Abstract] [Full Text] [PDF]


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