{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,30]],"date-time":"2026-08-30T02:33:31Z","timestamp":1788057211835,"version":"build-2784847793"},"reference-count":20,"publisher":"Oxford University Press (OUP)","issue":"5","license":[{"start":{"date-parts":[[2023,7,20]],"date-time":"2023-07-20T00:00:00Z","timestamp":1689811200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/academic.oup.com\/pages\/standard-publication-reuse-rights"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2023,9,7]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:sec>\n                  <jats:title>Background<\/jats:title>\n                  <jats:p>Free triiodothyronine (fT3) testing is most useful when thyroid stimulating hormone (TSH) is suppressed, and free thyroxine (fT4) is normal or decreased. These laboratory values in a symptomatic patient are referred to as T3 thyrotoxicosis. Standards for fT3 reflex testing have not been established. Herein, we examined the clinical utility of fT3 with the goal of identifying a TSH cutoff in the context of normal\/decreased fT4 that maximizes the utility of measuring fT3.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Methods<\/jats:title>\n                  <jats:p>TSH, fT4, and fT3 results between January 2016 and October 2021 were extracted from the laboratory information system and grouped if resulted on the same day for the same patient. Frequency of biochemical T3 thyrotoxicosis was evaluated at different TSH cutoffs and in outpatient vs inpatient settings.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>Of the 4366 TSH-fT4-fT3 results, 70 (1.6%) were consistent with biochemical T3 thyrotoxicosis. The common reasons were previously diagnosed hyperthyroidism on antithyroid medication (n = 28) or hypothyroidism on thyroid medication (n = 18) and newly diagnosed hyperthyroidism (n = 20, 0.5%). The likelihood of detecting T3 thyrotoxicosis increased with lower TSH cutoff (&amp;lt;0.3 \u03bcIU\/mL, 10.3% vs &amp;lt;0.0 1\u03bcIU\/mL, 27.6%). All patients with newly diagnosed hyperthyroidism had TSH &amp;lt;0.01 \u03bcIU\/mL. Higher frequency of T3 thyrotoxicosis was observed in the outpatient setting (34%) relative to the inpatient setting (14%, P &amp;lt; 0.001) when TSH &amp;lt; 0.01 \u03bcIU\/mL.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Conclusions<\/jats:title>\n                  <jats:p>T3 thyrotoxicosis is a relatively rare diagnosis and fT3 measurement has limited utility in the vast majority of patients. A fT3 reflex for patients with TSH &amp;lt;0.01 \u03bcIU\/mL and normal\/low fT4 may improve clinical utility and reduce unnecessary testing, especially in the outpatient setting.<\/jats:p>\n               <\/jats:sec>","DOI":"10.1093\/jalm\/jfad032","type":"journal-article","created":{"date-parts":[[2023,7,20]],"date-time":"2023-07-20T21:43:25Z","timestamp":1689889405000},"page":"847-855","source":"Crossref","is-referenced-by-count":4,"title":["Limited Utility of Free Triiodothyronine Testing"],"prefix":"10.1093","volume":"8","author":[{"given":"Yanchun","family":"Lin","sequence":"first","affiliation":[{"name":"Department of Pathology & Immunology, Washington University in St. Louis School of Medicine , St. Louis, MO , United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Amy E","family":"Riek","sequence":"additional","affiliation":[{"name":"Department of Medicine, Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine , St. Louis, MO , United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ann M","family":"Gronowski","sequence":"additional","affiliation":[{"name":"Department of Pathology & Immunology, Washington University in St. Louis School of Medicine , St. Louis, MO , United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Christopher W","family":"Farnsworth","sequence":"additional","affiliation":[{"name":"Department of Pathology & Immunology, Washington University in St. Louis School of Medicine , St. Louis, MO , United States"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"286","published-online":{"date-parts":[[2023,7,20]]},"reference":[{"key":"2023090701031871600_jfad032-B1","author":"American Thyroid Association"},{"key":"2023090701031871600_jfad032-B2","doi-asserted-by":"crossref","first-page":"91","DOI":"10.1385\/1-59259-986-9:91","volume-title":"Hormone assays in biological fluids.","author":"Squire","year":"2006"},{"key":"2023090701031871600_jfad032-B3","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1056\/NEJM198201073060107","article-title":"Thyroid-pituitary interaction","volume":"306","author":"Bleich","year":"1982","journal-title":"N Engl J Med"},{"key":"2023090701031871600_jfad032-B4","doi-asserted-by":"crossref","first-page":"1151","DOI":"10.1210\/jc.2015-4011","article-title":"Reconciling the log-linear and non\u2013log-linear nature of the TSH-free T4 relationship: intra-individual analysis of a large population","volume":"101","author":"Rothacker","year":"2016","journal-title":"J Clin Endocrinol Metab"},{"key":"2023090701031871600_jfad032-B5","doi-asserted-by":"crossref","first-page":"3","DOI":"10.3343\/alm.2019.39.1.3","article-title":"Laboratory testing in thyroid conditions\u2014pitfalls and clinical utility","volume":"39","author":"Soh","year":"2019","journal-title":"Ann Lab Med"},{"key":"2023090701031871600_jfad032-B6","doi-asserted-by":"crossref","first-page":"526","DOI":"10.1001\/archinte.1989.00390030032006","article-title":"Sensitivity, specificity, and cost-effectiveness of the sensitive thyrotropin assay in the diagnosis of thyroid disease in ambulatory patients","volume":"149","author":"De los Santos","year":"1989","journal-title":"Arch Intern Med"},{"key":"2023090701031871600_jfad032-B7","doi-asserted-by":"crossref","first-page":"1343","DOI":"10.1089\/thy.2016.0229","article-title":"American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis","volume":"2016","author":"Ross","year":"2016","journal-title":"Thyroid"},{"key":"2023090701031871600_jfad032-B8","doi-asserted-by":"crossref","first-page":"1573","DOI":"10.1001\/archinte.160.11.1573","article-title":"American Thyroid Association guidelines for detection of thyroid dysfunction","volume":"160","author":"Ladenson","year":"2000","journal-title":"Arch Intern Med"},{"key":"2023090701031871600_jfad032-B9","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1016\/j.clinbiochem.2020.05.004","article-title":"Reducing free thyroid hormone testing through multiple plan-do-study-act cycles","volume":"81","author":"Taher","year":"2020","journal-title":"Clin Biochem"},{"key":"2023090701031871600_jfad032-B10","doi-asserted-by":"crossref","first-page":"1898","DOI":"10.1515\/cclm-2016-1049","article-title":"Evaluation of thyroid test utilization through analysis of population-level data","volume":"55","author":"Gill","year":"2017","journal-title":"Clin Chem Lab Med"},{"key":"2023090701031871600_jfad032-B11","doi-asserted-by":"crossref","first-page":"229","DOI":"10.1016\/0002-9343(94)90147-3","article-title":"The clinical evaluation of patients with subclinical hyperthyroidism and free triiodothyronine (free T3) toxicosis","volume":"96","author":"Figge","year":"1994","journal-title":"Am J Med"},{"key":"2023090701031871600_jfad032-B12","doi-asserted-by":"crossref","first-page":"531","DOI":"10.1016\/0002-9343(90)90435-G","article-title":"Free triiodothyronine toxicosis: a distinct entity","volume":"88","author":"Bitton","year":"1990","journal-title":"Am J Med"},{"key":"2023090701031871600_jfad032-B13","doi-asserted-by":"crossref","first-page":"100","DOI":"10.1016\/0002-9343(91)90083-A","article-title":"Free T3 toxicosis: a distinct entity?","volume":"91","author":"Sakata","year":"1991","journal-title":"Am J Med"},{"key":"2023090701031871600_jfad032-B14","doi-asserted-by":"crossref","first-page":"1492","DOI":"10.1172\/JCI61231","article-title":"Coordination of hypothalamic and pituitary T3 production regulates TSH expression","volume":"123","author":"Fonseca","year":"2013","journal-title":"J Clin Invest"},{"key":"2023090701031871600_jfad032-B15","doi-asserted-by":"crossref","first-page":"4235","DOI":"10.1210\/jc.2017-01322","article-title":"Rationalizing thyroid function testing: which TSH cutoffs are optimal for testing free T4?","volume":"102","author":"Henze","year":"2017","journal-title":"J Clin Endocrinol Metab"},{"key":"2023090701031871600_jfad032-B16","doi-asserted-by":"crossref","first-page":"11","DOI":"10.1093\/ajcp\/105.1.11","article-title":"An algorithmic approach to thyroid function testing in a managed care setting: 3-year experience","volume":"105","author":"Feldkamp","year":"1996","journal-title":"Am J Clin Pathol"},{"key":"2023090701031871600_jfad032-B17","author":"Mayo Clinic Labs"},{"key":"2023090701031871600_jfad032-B18","first-page":"1572","volume-title":"Tietz textbook of clinical chemistry and molecular diagnostics","author":"Freedman","year":"2018","edition":"6th Ed."},{"key":"2023090701031871600_jfad032-B19","doi-asserted-by":"crossref","first-page":"1232","DOI":"10.1089\/thy.2017.0190","article-title":"Multi-center benchmark study reveals significant variation in thyroid testing in United States","volume":"27","author":"Lin","year":"2017","journal-title":"Thyroid"},{"key":"2023090701031871600_jfad032-B20","volume-title":"Ligand Assay General Survey. 2022 surveys and anatomic pathology education programs","author":"College of American Pathologists","year":"2021"}],"container-title":["The Journal of Applied Laboratory Medicine"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/academic.oup.com\/jalm\/article-pdf\/8\/5\/847\/51337098\/jfad032.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/academic.oup.com\/jalm\/article-pdf\/8\/5\/847\/51337098\/jfad032.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2023,9,7]],"date-time":"2023-09-07T01:04:15Z","timestamp":1694048655000},"score":1,"resource":{"primary":{"URL":"https:\/\/academic.oup.com\/jalm\/article\/8\/5\/847\/7227127"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,7,20]]},"references-count":20,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2023,7,20]]},"published-print":{"date-parts":[[2023,9,7]]}},"URL":"https:\/\/doi.org\/10.1093\/jalm\/jfad032","relation":{},"ISSN":["2475-7241"],"issn-type":[{"value":"2475-7241","type":"electronic"}],"subject":[],"published-other":{"date-parts":[[2023,9]]},"published":{"date-parts":[[2023,7,20]]}}}