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

Anja Kessler,David Bunk,John Marriot,Katleen Van Uytfanghe,Linda M Thienpont,Lothar Siekmann,Peter Stokes,Susan Tai

doi:10.1373/clinchem.2004.041772

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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. 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. All cRMLs performed the cRMPs with fulfillment of the predefined specifications: total and between-laboratory CVs < or =2.0% and 2.5%, respectively, and a systematic deviation < or =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%. 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 Systeme International d'Unites is needed.

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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)
The International Committee of Weights and Measures, the IFCC, and the International Laboratory Accreditation Cooperation agreed to cooperate toward the establishment of a Joint Committee for Traceability in Laboratory Medicine (JCTLM) (15 ), with the mission statement to categorize higher order reference materials and reference measurement procedures (RMPs) and to establish criteria and processes assessing the competencies required for laboratories performing the RMPs
We deal with the project’s efforts to organize the candidate reference measurement laboratories in a network, which required establishment of and agreement on a process to assess proper performance of the members of the project group at the inception of the network and of candidate members subsequently applying for admittance

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Endocrinology and Metabolism

Metrologic Traceability of Total Thyroxine Measurements in Human Serum: Efforts to Establish a Network of Reference Measurement Laboratories. Thienpont,1* Katleen Van Uytfanghe,[1] John Marriot,[2] Peter Stokes,[2] Lothar Siekmann,[3] Anja Kessler,[3] David Bunk,[4] and Susan Tai[4]

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