Abstract 120: Effect of biotin on thyroid function test

Background: Biotin is a readily available supplement that is a part of the B-complex vitamins and is sold overthecounter alone or in combination with other vitamins and minerals to improve skin, nail and hair health. Exogenous biotin intake is becoming a common cause of apparent abnormal thyroid function tests in medical practice. Case Report: A 50-year-old lady came to the medical OPD with reports of a “whole body test profile” which showed low TSH andhighT3 and T4. She had no symptoms suggestive thyrotoxicosis or hypothyroidism apart from hair thinning. There was no past medical or family history of thyroid disorder. Examination showed a clinically euthyroid state with no goitre. Repeat testing showed high fT3, fT4, and low TSH and -ve TSH receptor antibody. On enquiring about any medicinal history, she admitted taking a supplement for the last 3 months for her hair fall, which had 500 mcg biotin in it. TFTs were repeated after stopping the supplement for 7 days which came out to be normal. Discussion: Biotin is an essential co-factor for five carboxylases involved in fatty acid synthesis and energy production. Increased Biotin use in the recent times, as anutritional supplement has led to an increase in the interference of lab tests. While excessive intake of Biotin is not toxic as such, but problems may result from erroneous diagnoses or missed diagnoses. The FDA has issued a warning about falsely normal troponin level in MI, due to Biotin interference. There is no in vivo relationship between biotin and thyroid hormones, but high dose biotin affects thyroid function test in vitro when assessed with immunoassays using streptavidin biotin immobilizing system. A common misdiagnosis due to apparently low TSH with or without raised T4 isthyrotoxicosis or thyroxine over-replacement. American Thyroid Association advises stopping biotin for two days before thyroid function test. This can avoid unnecessary investigations, patient anxiety, and healthcare costs. Patients can continue to take biotin except stopping it temporarily before thyroid blood tests. Conclusion: Biotin interference mimics the laboratory changes in thyrotoxicosis. Prompt recognition of biotin interference requires a high index of suspicion. History of medicine intake including health supplements having biotin is important in patients showing mismatch of lab and clinical findings of thyrotoxicosis as it minimizes unnecessary expensive additional work up and treatment.