High-Dose Biotin Treatment for Secondary Progressive Multiple Sclerosis May Interfere with Thyroid Assays

ABSTRACT Objective: To review cases and increase awareness in clinicians treating patients who may be taking biotin. Methods: We describe the presentation and workup of a woman with secondary progressive multiple sclerosis on high-dose biotin, with laboratory studies suggestive of thyrotoxicosis. Results: Plasma samples showed laboratory evidence of elevated thyroid hormone levels, with elevated free thyroxine >7.8 ng/dL (reference interval [RI], 0.9 to 1.7 ng/dL) and decreased thyroid-stimulating hormone <0.02 μIU/mL (RI, 0.5 to 5.7 μIU/mL). Laboratory values normalized when biotin was withheld prior to repeat testing. Conclusion: Our case report demonstrates that ingestion of high-dose biotin in multiple sclerosis patients can cause interference with laboratory assessment of thyroid function. This interference causes laboratory values suggestive of thyrotoxicosis and can lead to unnecessary evaluation. Clinicians should be aware of the risk of laboratory interference in this patient demographic. Abbreviations: MS = multiple sclerosis; TSH = thyroid-stimulating hormone; T3 = triiodothyronine; T4 = thyroxine