{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,29]],"date-time":"2026-04-29T02:09:34Z","timestamp":1777428574948,"version":"3.51.4"},"reference-count":39,"publisher":"SAGE Publications","issue":"6","license":[{"start":{"date-parts":[[1990,11,1]],"date-time":"1990-11-01T00:00:00Z","timestamp":657417600000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.sagepub.com\/page\/policies\/text-and-data-mining-license"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Ann Clin Biochem"],"published-print":{"date-parts":[[1990,11]]},"abstract":"<jats:p>\n                    Plasma or serum free thyroxine (T\n                    <jats:sub>4<\/jats:sub>\n                    ) was measured by a novel non-isotopic, two-step immunossay in 373 consecutive patients attending a thyroid clinic, in whom thyroid status was categorized according to clinical findings, supported by routine thyroid function tests. The 95% confidence limit of free T\n                    <jats:sub>4<\/jats:sub>\n                    in the euthyroid patients ( n = 112) was 7\u201320 pmol\/L. Free T\n                    <jats:sub>4<\/jats:sub>\n                    concentrations within the reference range were found in six of 40 patients with primary hypothyroidism and nine of 182 patients with overt thyrotoxicosis, six of whom had T\n                    <jats:sub>3<\/jats:sub>\n                    toxicosis. Serum or plasma free T\n                    <jats:sub>4<\/jats:sub>\n                    measured by the two-step method showed improved diagnostic specificity over an analogue RIA in selected groups of euthyroid patients in whom abnormal binding of analogue T\n                    <jats:sub>4<\/jats:sub>\n                    can affect the validity of the result. Free T\n                    <jats:sub>4<\/jats:sub>\n                    results found by analogue RIA and the two-step method in 58 patients who were receiving thyroxine replacement therapy were similar. The between-assay precision of the two-step method was poor ranging from a coefficient of variation of 9\u00b77% to 19\u00b73% over a free T\n                    <jats:sub>4<\/jats:sub>\n                    concentration range of 5\u00b70 to 46\u00b70 pmol\/L. We conclude that the two-step methodology offers diagnostic advantages for a laboratory which receives specimens from such patients for exclusion of thyroid disease but that improved assay precision is required before it could be used in a routine situation.\n                  <\/jats:p>","DOI":"10.1177\/000456329002700610","type":"journal-article","created":{"date-parts":[[2014,2,5]],"date-time":"2014-02-05T16:58:39Z","timestamp":1391619519000},"page":"581-591","source":"Crossref","is-referenced-by-count":5,"title":["Non-Isotopic, Two-Step Free Thyroxine Immunoassay: A Better Measure of Free Thyroxine than Analogue Radioimmunoassay"],"prefix":"10.1177","volume":"27","author":[{"given":"G J","family":"Beckett","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"W A","family":"Ratcliffe","sequence":"additional","affiliation":[{"name":"Wolfson Research Laboratories, Department of Clinical Chemistry, Queen Elizabeth Medical Centre, Edgbaston, Birmingham B15 2TH, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"B","family":"Chapman","sequence":"additional","affiliation":[{"name":"Geriatric Assessment Unit, The Royal Infirmary, Edinburgh EH3 9YW, Scotland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"P","family":"Wu","sequence":"additional","affiliation":[{"name":"Endocrine Clinic, The Royal Infirmary, Edinburgh EH3 9YW, Scotland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"P W H","family":"Rae","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"S M","family":"Gow","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"A D","family":"Toft","sequence":"additional","affiliation":[{"name":"Endocrine Clinic, The Royal Infirmary, Edinburgh EH3 9YW, 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