What is the impact of biotin on thyroid replacement therapy (TRT)?

Biotin Causes Significant Laboratory Interference with Thyroid Function Tests, Not True Physiologic Effects on Thyroid Replacement Therapy

Biotin does not affect thyroid replacement therapy itself, but it causes false laboratory results in thyroid function tests through assay interference, potentially leading to misdiagnosis and inappropriate treatment changes. The interference is analytical, not physiological—biotin disrupts the streptavidin-biotin binding used in immunoassays, creating spurious results that can mimic hyperthyroidism or other thyroid disorders 1, 2.

Mechanism of Interference

• Biotin interferes with immunoassays that use streptavidin-biotin binding technology to detect thyroid hormones 1, 2
• The interference is bidirectional: it can cause falsely low TSH and falsely elevated free T4, free T3, and total T3 values, creating a laboratory pattern that mimics Graves' disease 2, 3, 4
• Thyroglobulin assays show negative interference (falsely low values), which is particularly problematic in thyroid cancer monitoring 2
• Non-biotin-based assays (such as TSH and total T4 on some platforms) may not be affected, creating inconsistent patterns that can help identify interference 3

Clinically Relevant Doses

• Doses as low as 10 mg daily cause significant assay interference within 2 hours of ingestion 2, 5
• Over-the-counter supplements commonly contain 5-10 mg, while prescription biotin for multiple sclerosis can reach 300 mg daily 1, 4
• Maximal interference occurs 2 hours after biotin ingestion on both day 1 and after chronic use (day 8) 2
• The interference resolves within 24-48 hours after biotin discontinuation 4

Platform-Specific Vulnerabilities

• Roche Cobas 6000: Shows significant interference in TSH, free T4, and total T3 measurements 2
• Siemens IMMULITE 2000: Demonstrates falsely low thyroglobulin levels 2
• Beckman DXI800: Shows positive interference with free T4, free T3, and total T3, but negative interference with thyroglobulin 3
• Abbott Architect: Generally less affected in the studied assays 2
• Mass spectrometry (LC-MS/MS) is not affected by biotin and can serve as a confirmatory method 2, 3

Clinical Recognition and Management

Key diagnostic clue: Elevated free T3 and free T4 with normal or suppressed TSH in an asymptomatic patient should raise suspicion for biotin interference 3, 5, 4

• Always ask patients about biotin supplementation before ordering thyroid function tests, as it is widely available over-the-counter for cosmetic purposes (hair, skin, nails) 1, 4
• Look for discordance between total T3 (falsely elevated) and total T4 (unaffected on some platforms), which indicates biotin interference 3
• Patients with thyroid cancer requiring careful thyroglobulin monitoring are at particular risk of inappropriate management due to falsely low thyroglobulin values 2

Management algorithm:

• Discontinue biotin for at least 48-72 hours before thyroid function testing 4
• If interference is suspected after testing, repeat thyroid function tests 24-48 hours after biotin cessation 4
• Consider using non-biotin-based assays or mass spectrometry for confirmation 2, 3
• Do not initiate or adjust thyroid medication based on discordant laboratory values in asymptomatic patients taking biotin 5, 4

Critical Pitfall

The most dangerous scenario occurs when patients on stable levothyroxine therapy take biotin supplements and undergo routine monitoring—the falsely suppressed TSH and elevated free T4 may prompt clinicians to inappropriately reduce levothyroxine doses, potentially causing iatrogenic hypothyroidism 4. Conversely, patients may be misdiagnosed with Graves' disease and started on unnecessary antithyroid medications 5, 4.