A caution regarding high-dose biotin therapy: misdiagnosis of hyperthyroidism in euthyroid patients

High-dose biotin therapy is finding favour as a promising novel agent in the treatment of multiple sclerosis.1 We feel compelled to alert clinicians to an easily overlooked aspect of biotin therapy that has the potential to cause significant harm: it causes profound interference with immunoassays that are based on streptavidin–biotin technology.2,3 Such assays are widely used in routine laboratories. Depending on the method principle, biotin interference may cause falsely high results (typically in competitive immunoassays) or falsely low results (typically in sandwich immunoassays).4 This interference may produce a pattern of results that closely resembles disease, leading to false diagnoses, inappropriate treatment and risk of complications.