Biotin beware: a brief overview of interference in some immunoassays

In 2015, a 55-year-old man with multiple sclerosis was referred to a hospital thyroid unit because the screening thyroid function tests showed markedly elevated FT4 and FT3 results and low (apparently suppressed) levels of thyroid-stimulating hormone (TSH).¹ This pattern of results typically suggests a severe form of Graves’ disease. However, a thyroid scan using iodine-123 (¹²³I) showed a normal thyroid gland with normal radioiodine uptake. The patient showed no symptoms of hyperthyroidism. As the biochemical results were discordant with the patient’s clinical assessment, investigations for assay interference from drugs or other compounds were conducted.

It emerged that the patient had taken very high doses of biotin (300 mg daily, roughly 1000 times the recommended daily intake) as a study had suggested that biotin might be beneficial for multiple sclerosis patients. The discontinuation of biotin supplements resulted in the FT4, FT3 and TSH results returning to within reference range values in just a few days. Further case studies and scientific articles of a similar nature have been published.^2,3

Just a few months ago, the US Food and Drug Administration (FDA) issued a Safety Communication⁴ to alert the public, healthcare providers and laboratory personnel that biotin, ingested in high-street health supplement form or administered as a clinical therapy, can interfere with certain laboratory tests and produce incorrect laboratory test results.