The clinical laboratory is instrumental in the diagnosis and monitoring of thyroid disease, which affects up to 20 million Americans. The American Thyroid Association observes Thyroid Awareness Month in January, to educate the public about thyroid health while encouraging medical education and research to improve diagnosis and treatment of thyroid disorders.

Thyroid testing is familiar to most laboratorians: even waived laboratories can screen patients for thyroid disease, as some small benchtop cartridge analyzers and single-use kit tests are approved for waived use by the FDA. Diagnosis is generally simple, with abnormal TSH or T4 results clearly indicating a problem. However, no test is completely immune to interference, and there has been some recent evidence that over-the-counter supplement use may be contributing to misdiagnosis of thyroid disease.

Many thyroid hormone tests are competitive immunoassays which use antibodies coupled with biotin, one of the B-vitamins, to trap and detect their target hormones. For the average patient, or even a patient taking a standard over-the-counter multivitamin containing biotin, there’s very little risk of serum biotin levels causing any interference with the assay. However, patients taking mega-doses of biotin supplements can have high enough levels of serum biotin to interfere with the assays: their lab results may be falsely elevated, sometimes quite significantly.

Common multivitamin blends don’t contain enough biotin to cause any concern, but concentrated biotin supplements are available for purchase online, often advertised as miracle products for hair and nail strength. Patients who take these supplements may be masking an underperforming thyroid, or could find themselves mistakenly diagnosed with hyperthyroidism. Unfortunately, because patients often consider supplements to be “natural,” they may neglect to mention them to their physicians when asked what medications they’re currently taking.

Luckily for patients who take biotin supplements, that vitamin is water-soluble and is flushed from the body very quickly. Once the patient is asked to stop taking the supplement, a repeat test ordered a few days later may come back completely normal.

As always, when test results don’t quite fit the patient’s clinical picture, the physician should consider possible interferences and limitations of the tests they’re using. It’s easy to see how a patient could be misdiagnosed with a thyroid problem, and possibly even unnecessarily treated for it, if unexpected laboratory results weren’t investigated. For laboratorians, it’s important to be aware of the limitations of the test methods used in your laboratory, so that you can answer questions about suspiciously out-of-line results.

About The Author

Jen is the Post Survey Team Leader with COLA, where she provides valuable consultation to laboratory clients regarding regulatory compliance and quality lab practices, and guides member laboratories through the Accreditation process. She is a licensed Medical Laboratory Scientist with over a decade of experience in high-volume hospital blood banks and core laboratories. She holds a Bachelor of Science degree in Human Physiology from McGill University and a Medical Technology degree from Dawson College. She is also a freelance science writer whose articles are featured on websites dedicated to consumer safety, STEM outreach, and science communication.