Erroneous thyroid diagnosis due to over-the-counter biotin

Biotin is a component of the vitamin B complex used in standard immunoassays to detect serum levels of various hormones and non-hormones, including thyrotropin (TSH) and thyroxine. These assays involve a strong bond between streptavidin and biotin, which serves as an anchor for measured analytes. Large doses of exogenous biotin for the treatment of certain medical conditions have resulted in assay interference, causing TSH to be spuriously lowered. Smaller doses of biotin found in dietary supplements also have caused assay interference.

We describe four cases in which over-the-counter (OTC) biotin caused erroneous thyroid diagnosis and clinical confusion in patients with preexisting thyroid disease. Serum TSH and thyroxine were measured by the Vitros 5600 assay.

Although the biotin-streptavidin interaction is sensitive for detecting serum levels of TSH, it is subject to interference by exogenous biotin at levels found in OTC products. The widespread use of OTC biotin for cosmetic purposes can adversely affect the diagnosis of the entire spectrum of functional thyroid disorders. Physicians must carefully and routinely question for the use of biotin before thyroid function testing.