Linde A C De Grande1, Katleen Van Uytfanghe2, Dries Reynders3, Barnali Das4, James D Faix5, Finlay MacKenzie6, Brigitte Decallonne7, Akira Hishinuma8, Bruno Lapauw9, Paul Taelman10, Paul Van Crombrugge11, Annick Van den Bruel12, Brigitte Velkeniers13, Paul Williams14, Linda M Thienpont15,16. 1. Department of Pharmaceutical Analysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium. 2. Ref4U, Laboratory of Toxicology, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium. 3. Department of Applied Mathematics, Computer Science and Statistics, Faculty of Sciences, Ghent University, Ghent, Belgium. 4. Biochemistry and Immunology Laboratory, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute, Mumbai, India. 5. Clinical Chemistry and Immunology, Montefiore Medical Center, and Department of Pathology, Albert Einstein School of Medicine, New York, NY. 6. Birmingham Quality/UK NEQAS, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK. 7. Department of Endocrinology, University Hospitals Leuven, Leuven, Belgium. 8. Department of Infection Control and Clinical Laboratory Medicine, Dokkyo Medical University, Tochigi, Japan. 9. Department of Endocrinology, Ghent University Hospital, Ghent, Belgium. 10. Laboratory of Endocrinology, Department of Laboratory Medicine, AZ Maria-Middelares Sint-Jozef, Campus Maria-Middelares, Ghent, Belgium. 11. Department of Endocrinology, OLV Ziekenhuis Aalst-Asse-Ninove, Aalst, Belgium. 12. Department of Endocrinology, General Hospital Sint Jan, Bruges, Belgium. 13. Department of Endocrinology, Universitair Ziekenhuis Brussel, Brussels, Belgium. 14. Department of Endocrinology, Royal Prince Alfred Hospital, Camperdown, Australia. 15. Department of Pharmaceutical Analysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium; linda.thienpont@ugent.be. 16. Thienpont & Stöckl Wissenschaftliches Consulting GbR, Rennertshofen (OT Bertoldsheim), Germany.
Abstract
BACKGROUND: The IFCC Committee for Standardization of Thyroid Function Tests intended to standardize free thyroxine (FT4) immunoassays. We developed a Système International d'Unités traceable conventional reference measurement procedure (RMP) based on equilibrium dialysis and mass spectrometry. We describe here the latest studies intended to recalibrate against the RMP and supply a proof of concept, which should allow continued standardization efforts. METHODS: We used the RMP to target the standardization and reference interval (RI) panels, which were also measured by 13 manufacturers. We validated the suitability of the recalibrated results to meet specifications for bias (3.3%) and total error (8.0%) determined from biological variation. However, because these specifications were stringent, we expanded them to 10% and 13%, respectively. The results for the RI panel were reported as if the assays were recalibrated. We estimated all but 1 RI using parametric statistical procedures and hypothesized that the RI determined by the RMP was suitable for use by the recalibrated assays. RESULTS: Twelve of 13 recalibrated assays had a bias, meeting the 10% specification with 95% confidence; for 7 assays, this applied even for the 3.3% specification. Only 1 assay met the 13% total error specification. Recalibration reduced the CV of the assay means for the standardization panel from 13% to 5%. The proof-of-concept study confirmed our hypothesis regarding the RI but within constraints. CONCLUSIONS: Recalibration to the RMP significantly reduced the FT4 immunoassays' bias, so that the RI determined by the RMP was suitable for common use within a margin of 12.5%.
BACKGROUND: The IFCC Committee for Standardization of Thyroid Function Tests intended to standardize free thyroxine (FT4) immunoassays. We developed a Système International d'Unités traceable conventional reference measurement procedure (RMP) based on equilibrium dialysis and mass spectrometry. We describe here the latest studies intended to recalibrate against the RMP and supply a proof of concept, which should allow continued standardization efforts. METHODS: We used the RMP to target the standardization and reference interval (RI) panels, which were also measured by 13 manufacturers. We validated the suitability of the recalibrated results to meet specifications for bias (3.3%) and total error (8.0%) determined from biological variation. However, because these specifications were stringent, we expanded them to 10% and 13%, respectively. The results for the RI panel were reported as if the assays were recalibrated. We estimated all but 1 RI using parametric statistical procedures and hypothesized that the RI determined by the RMP was suitable for use by the recalibrated assays. RESULTS: Twelve of 13 recalibrated assays had a bias, meeting the 10% specification with 95% confidence; for 7 assays, this applied even for the 3.3% specification. Only 1 assay met the 13% total error specification. Recalibration reduced the CV of the assay means for the standardization panel from 13% to 5%. The proof-of-concept study confirmed our hypothesis regarding the RI but within constraints. CONCLUSIONS: Recalibration to the RMP significantly reduced the FT4 immunoassays' bias, so that the RI determined by the RMP was suitable for common use within a margin of 12.5%.