FRI518 Good For Hair, Skin, And Nails But Bad For Thyroid Lab Tests

Disclosure: S. Khan: None. P. Kachhadia: None. S. Aldasouqi: None. A. Abu Limon: None. Introduction: Biotin also known as Vitamin B7 is very commonly used for hair, skin and nail growth. It can cause falsely high levels of free thyroxine (FT4), and free triiodothyronine (FT3) and falsely low thyroid stimulating hormone (TSH) levels. This can lead to a false diagnosis of hyperthyroidism. The ATA has recommended to stop taking biotin at least 2 days prior to lab testing to avoid spurious results. We present a case of a patient with hypothyroidism on a stable dose of levothyroxine who developed abnormal thyroid function tests (TFTs) due to biotin supplements. Case Presentation: A 57 years old female with long-standing hypothyroidism had been a on stable dose of Levothyroxine, 100 mcg daily. She was compliant with treatment. Her TFTs, done on periodic follow ups every 3-6 months were normal. Recently, on semi-annual lab work, thyroid function tests revealed elevated free T4 and T3, but normal TSH values. The patient was clinically euthyroid. Due to the unexpected thyroid function test result which did not portray clinical hyperthyroidism, repeat detailed history was taken which revealed that the patient was taking Biotin 1000 mg twice daily, as a hair-skin-nail beauty product. TFTs were repeated after she was instructed to stop Biotin for 3 days, which resulted in normal values. Patient was well-educated by our team to stop Biotin before labs, in the future. Once again, close to a year later, TFTs showed elevated FT4 and borderline low TSH. When contacted, she admitted forgetting to stop Biotin before labs. Labs off biotin once more showed normalization of FT4. Discussion: A variety of laboratory immunoassay blood tests utilize Biotin (Vitamin B7) in view of its high affinity to Streptavidin. At physiological concentrations, Biotin does not interfere with thyroid function tests. However, excessive Biotin use which is often taken as a beauty supplement is known to interfere with these tests. Typically, excessive Biotin intake will result in falsely elevated T4 and T3 and falsely low TSH. Furthermore, it will result in falsely elevated immunoglobulins that are markers for Graves’ disease. Our patient was taking a total of 2000mcg of biotin daily over the counter. This interference, which is not uncommon in clinical practice, has led to many misdiagnoses with potential for unnecessary workup, and sometimes initiation of inappropriate or potentially harmful treatment regimens. In this case report, though this patient’s thyroid function test results were suggestive of hyperthyroidism, biotin use is what caused in-vitro interference with the Biotin-Streptavidine Immunoassay. For this reason, clinicians should remain attentive to common biotin use in patients and advise them to hold biotin at least 2 days before labwork to avoid such outcomes. Furthermore, lab centers should also be informed of this interference and should avoid lab draw in those patients did that not hold biotin appropriately. Presentation: Friday, June 16, 2023