Will taking biotin (B-complex vitamin) 2 tablets daily interfere with thyroid function tests in a patient with a history of hyperthyroidism?

Biotin Interference with Thyroid Function Tests in Hyperthyroidism Patients

Critical Warning: Biotin Causes False Thyroid Test Results

Taking biotin 2 tablets daily will significantly interfere with thyroid function tests, potentially causing falsely suppressed TSH and falsely elevated free T4/T3 levels that mimic hyperthyroidism, leading to dangerous misdiagnosis and inappropriate treatment. 1, 2, 3

Mechanism of Interference

• Biotin interferes with immunoassays that use biotin-streptavidin chemistry, which is the standard method for measuring TSH, free T4, free T3, and thyroglobulin 4, 2
• Depending on the assay design (competitive vs. sandwich method), biotin can cause either falsely low or falsely high results 4
• The Roche Cobas 6000 platform shows particularly significant interference with TSH, free T4, and total T3 measurements after biotin exposure 2
• Even standard over-the-counter biotin doses (not just high-dose therapy) cause clinically significant assay interference 5

Specific Impact on Thyroid Tests

• TSH: Falsely suppressed/lowered, mimicking hyperthyroidism 1, 2, 3, 5, 6
• Free T4: Falsely elevated 1, 2, 3, 6
• Free T3: Falsely elevated 3, 6
• Thyroglobulin: Falsely lowered when measured with Siemens IMMULITE 2000 2

Timeline of Interference

• Maximum interference occurs 2 hours after biotin ingestion on both day 1 and day 8 of supplementation 2
• Interference persists with daily dosing at 10 mg/day for at least 8 days 2
• Thyroid function tests normalize within 5-7 days after biotin discontinuation 1, 3

Clinical Consequences in Your Case

• A patient with history of hyperthyroidism taking biotin will have laboratory results that falsely suggest active hyperthyroidism or inadequate treatment 1, 3, 5
• This can lead to inappropriate initiation or escalation of antithyroid medications (methimazole or propylthiouracil) 3
• Patients may be misdiagnosed with Graves' disease when they are actually euthyroid 1
• For thyroid cancer patients requiring TSH suppression, biotin interference makes accurate levothyroxine titration impossible 2

Mandatory Action Steps

Before Any Thyroid Testing:

1. Discontinue biotin for at least 5-7 days before thyroid function testing 1, 3
2. Document biotin use in the medical record and communicate with the laboratory 1
3. Verify which assay platform your laboratory uses, as interference varies by manufacturer 2

If Already on Antithyroid Medications:

• Do NOT adjust antithyroid drug doses based on thyroid function tests obtained while taking biotin 2, 3
• If clinical examination shows no signs of hyperthyroidism (no tachycardia, tremor, weight loss, heat intolerance) but labs suggest hyperthyroidism, suspect biotin interference 1, 6
• Stop biotin for 5-7 days and repeat thyroid function tests before making any treatment changes 1, 3

Critical Pitfalls to Avoid

• Never assume normal biotin supplementation is safe for thyroid testing—even standard over-the-counter doses cause interference 5
• Do not rely on patient disclosure—many patients do not consider biotin a "medication" and fail to report it 3, 5
• Routinely ask about biotin use before ordering thyroid function tests, especially in patients with preexisting thyroid disease 5
• Recognize the discrepancy: When laboratory results suggest severe thyrotoxicosis but clinical examination is completely normal, biotin interference is the likely explanation 1, 6

Alternative Testing Strategies

• Liquid chromatography with tandem mass spectrometry (LC-MS/MS) is not affected by biotin interference and can be used if biotin cannot be discontinued 2
• However, LC-MS/MS is not widely available for routine thyroid function testing 2

Special Considerations for Hyperthyroidism Monitoring

• For patients requiring careful thyroid hormone monitoring (thyroid cancer, Graves' disease on antithyroid drugs), biotin supplementation should be permanently discontinued 2
• If biotin is medically necessary (e.g., high-dose therapy for multiple sclerosis), coordinate with the laboratory to use non-biotin-based assays or ensure adequate washout periods 1, 2
• The 5-7 day washout period must be strictly observed before any thyroid function testing used for treatment decisions 1, 3