Biotin’s Effect on Thyroid Function Tests
Biotin, also known as vitamin B7, plays a role in metabolizing fats, carbohydrates, and amino acids needed for protein synthesis. It is commonly found in various health supplements, including multivitamins, prenatal vitamins, and products promoting hair, skin, and nail health. Biotin can potentially disrupt thyroid function tests that rely on a biotin/streptavidin interaction. Depending on the test’s design, this interference can lead to either artificially low or high test results, which may result in incorrect patient management or diagnosis. The risk of interference increases with higher biotin doses. Healthcare professionals should be cautious and consider the possibility of biotin interference when interpreting results from thyroid immunoassays, particularly when the results do not align with the patient’s clinical symptoms.
Mechanism Behind Biotin Interference
Thyroid function tests are vital for assessing thyroid hormone levels, including thyroxine (T4), triiodothyronine (T3), and thyroid stimulating hormone (TSH), used in diagnosing and monitoring thyroid disorders like hyperthyroidism and hypothyroidism. Two types of thyroid immunoassays are commonly employed: the sandwich assay for larger molecules such as TSH and the competitive assay for smaller molecules like T3 and T4. Both assays rely on the specific binding between biotin and streptavidin (a glycoprotein) as a detection method. Exogenous biotin, which can come from supplements like those for hair, skin, and nails, can disrupt both assay types, causing either falsely low or high results, depending on the assay’s design. This interference has been observed in oral products with ≥ 150 mcg biotin per dose unit and parenteral products with ≥ 60 mcg biotin per dose unit.
In a TSH sandwich assay, excess biotin occupies streptavidin binding sites, preventing the TSH-antibody sandwich complex from forming and leading to falsely low results (Figure 1A).
In competitive immunoassays, where endogenous analytes (T3 or T4) compete with labeled analytes for biotinylated antibody binding sites, excess biotin causes falsely high results. Biotin hinders the binding of antibody-labeled analytes and antibody-endogenous analytes to the streptavidin-coated solid phase. Unbound antibodies are subsequently removed during the wash step, eliminating any signal indicating the endogenous analyte’s concentration. Because serum endogenous analyte concentration is inversely related to signal intensity, this results in falsely elevated values (Figure 1B).
Biotin interference with thyroid immunoassays is a well-documented phenomenon, leading to misdiagnoses or incorrect management of thyroid disorders, as these tests are critical for initiating or adjusting thyroid medications.
Regulatory Actions
In November 2022, the European Medicines Agency’s (EMA) Pharmacovigilance Risk Assessment Committee (PRAC) recommended adding new warnings regarding biotin interference with thyroid function tests to the product information of levothyroxine-containing products. This recommendation followed their review, which considered information from spontaneous reports and the medical literature.
Local Measures
In 2019, the Health Sciences Authority (HSA) evaluated the potential interference of biotin with clinical laboratory tests, including thyroid function tests. HSA collaborated with relevant companies to include warnings about possible interference in the local package inserts (PIs) of parenteral biotin-containing products. This information was communicated to healthcare professionals through an article in the ADR News Bulletin’s September 2019 issue.
Recognizing that this safety concern might also impact patients using levothyroxine therapy, HSA worked with product registrants to introduce similar warnings about the possibility of biotin interference with thyroid function tests in the local PIs of levothyroxine products.
As of now, HSA has not received any reports of local adverse events related to biotin interference causing incorrect thyroid function test results.
HSA’s Recommendation
Healthcare professionals are advised to remain vigilant about the potential for biotin interference when interpreting thyroid function test results, especially if there is a discrepancy with the observed clinical symptoms. This may involve inquiring about their patients’ use of biotin health supplements, including those marketed for improving hair, skin, and nail health.
HSA: Health Sciences Authority; EMA: European Medicines Agency; PRAC: Pharmacovigilance Risk Assessment Committee; PI: Package Inserts
Biotin: Vitamin B7; T4: thyroxine , T3: triiodothyronine; TSH: thyroid stimulating hormone
Link to the HSA announcement: https://www.hsa.gov.sg/announcements/safety-alert/reminder-on-the-risk-of-pholcodine-associated-perioperative-anaphylaxis-with-neuromuscular-blocking-agents
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