{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,16]],"date-time":"2026-03-16T20:57:10Z","timestamp":1773694630180,"version":"3.50.1"},"reference-count":24,"publisher":"Oxford University Press (OUP)","issue":"9","license":[{"start":{"date-parts":[[2006,9,1]],"date-time":"2006-09-01T00:00:00Z","timestamp":1157068800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/academic.oup.com\/journals\/pages\/open_access\/funder_policies\/chorus\/standard_publication_model"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2006,9,1]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:p>Background: Serum-free thyroxine (FT4) testing is recommended for diagnosis or monitoring of thyroid dysfunction, particularly in cases of hormone binding abnormalities. However, the poor intermethod agreement among commercial FT4 assays suggests a need for standardization with a hierarchically higher measurement procedure. To that purpose, we applied equilibrium dialysis (ED) in combination with isotope dilution-liquid chromatography\/tandem mass spectrometry (ID-LC-tandem MS).<\/jats:p>\n               <jats:p>Methods: After ED, we collected dialysate into tubes containing [13C6]-T4 for ID and [13C9]-T4 as carrier, purified the samples by solid-phase extraction, and analyzed them with LC\/tandem MS. We evaluated the procedure\u2019s analytical performance and tested its suitability for measurement of hypo-, eu-, and hyperthyroid serum FT4 concentrations. We conducted a pilot method comparison study with 3 commercial assays to investigate whether frozen sera could be used for the purpose of FT4 standardization.<\/jats:p>\n               <jats:p>Results: The within-run, between-run, and total CVs (inclusive ED) were 3.7%, 4.2%, and 5.6%, respectively (17.7 pmol\/L; n = 20). The mean accuracy, estimated from recovery experiments with dialysate and dialysis buffer supplemented at 8.7, 18.7, and 33.5 pmol\/L, and from analysis of certified sera gravimetrically diluted to 9.8, 19.2, and 34.8 pmol\/L, was 98.0% to 102.8%. The procedure\u2019s limit of detection and limit of quantification were 0.5 and 1.3 pmol\/L, respectively. The method comparison demonstrated the suitability of the selected sera for standardization of FT4 assays and confirmed the lack of assay comparability.<\/jats:p>\n               <jats:p>Conclusions: We demonstrated that the described ED-ID-LC\/tandem MS procedure and the selected type of sera qualify for standardization of FT4 measurements.<\/jats:p>","DOI":"10.1373\/clinchem.2006.070425","type":"journal-article","created":{"date-parts":[[2006,7,14]],"date-time":"2006-07-14T00:52:27Z","timestamp":1152838347000},"page":"1817-1821","source":"Crossref","is-referenced-by-count":36,"title":["Use of Frozen Sera for FT4 Standardization: Investigation by Equilibrium Dialysis Combined with Isotope Dilution-Mass Spectrometry and Immunoassay"],"prefix":"10.1093","volume":"52","author":[{"given":"Katleen","family":"Van Uytfanghe","sequence":"first","affiliation":[{"name":"Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium; Department of Chemical Endocrinology, University Medical Centre, Nijmegen, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Dietmar","family":"Sto\u0308ckl","sequence":"first","affiliation":[{"name":"Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium; Department of Chemical Endocrinology, University Medical Centre, Nijmegen, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"H Alec","family":"Ross","sequence":"first","affiliation":[{"name":"Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium; Department of Chemical Endocrinology, University Medical Centre, Nijmegen, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Linda M","family":"Thienpont","sequence":"first","affiliation":[{"name":"Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium; Department of Chemical Endocrinology, University Medical Centre, Nijmegen, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"286","published-online":{"date-parts":[[2006,9,1]]},"reference":[{"key":"2020022801241061700_R1","doi-asserted-by":"crossref","unstructured":"Ladenson PW, Singer PA, Ain KB, Bagchi N, Bigos ST, Levy EG. 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