• B Bouillet and A Rouland.
• Service d'endocrinologie, diabétologie et maladies métaboliques, centre hospitalier universitaire, 21079 Dijon, France; Unité Inserm LNC-UMR 1231, université de Bourgogne, 21000 Dijon, France. Electronic address: benjamin.bouillet@chu-dijon.fr.
• Rev Med Interne. 2020 Feb 1; 41 (2): 123-125.

IntroductionMany hormone immunoassays use the biotin streptavidin interaction to immobilize immune complexes. The intake of high dose biotin can interfere with immunoassays using the biotin streptavidin interaction. The biotin-immunoassay interference generates falsely low or falsely high tests of hormones according to the type of immunoassay used.Case ReportA 70-year-old patient, with progressive multiple sclerosis, was referred to our hospital for thyrotoxicosis. She was found to have markedly elevated thyroid hormones level (T3-T4) and decreased thyrotropin (TSH) level but she had no symptoms of hyperthyroidism. An ingestion of biotin, that is more and more frequent in patients with progressive multiple sclerosis, was found. Thyroid function tests normalized after discontinuation of biotin treatment.ConclusionThe discrepancy between a clinical exam which is not indicative of thyrotoxicosis and markedly abnormal thyroid function tests should lead to a search for biotin intake, which can interfere with thyroid function tests.Copyright © 2019 Société Nationale Française de Médecine Interne (SNFMI). Published by Elsevier Masson SAS. All rights reserved.

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