Misdiagnosis of Graves' Disease with Apparent Severe Hyperthyroidism in a Patient Taking Biotin Megadoses

Background: Accurate immunoassays measuring minute quantities of hormones are the cornerstone of the practice of endocrinology. Despite tremendous advances in this field, novel pitfalls in these tests emerge from time to time. Oral biotin can interfere with immunoassays of several hormones. The purpose of this report is to relate an extreme case of such interference. Patient findings: A patient with progressive multiple sclerosis was found to have extremely elevated free thyroxine, triiodothyronine, and suppressed thyrotropin (TSH) levels. His TSH receptor binding inhibiting antibody level was also elevated. This constellation of laboratory findings suggested a diagnosis of severe Graves' disease. All of the assays yielding abnormal results employed the biotin–streptavidin affinity in their design. The patient had no symptoms of hyperthyroidism, and detailed review of his medications revealed intake of megadoses of biotin. Temporary discontinuation of biotin treatment resulted in complete resolution of th...