When thyroid labs do not add up, physicians should ask patients about biotin supplements.

Area of Science:

• Endocrinology
• Clinical Chemistry

Background:

• Levothyroxine is a common treatment for hypothyroidism, often following radioactive iodine ablation for Graves' disease.
• Maintaining stable thyroid hormone levels is crucial for patient well-being and requires accurate laboratory monitoring.

Observation:

• A patient with a history of Graves' disease on stable levothyroxine therapy presented with unexplained, fluctuating thyroid function tests.
• Initial extensive evaluations failed to identify a cause for the abnormal thyroid lab results.

Findings:

• The patient was found to be taking high-dose biotin supplements (10 mg twice daily).
• Biotin interference with immunoassays is a recently recognized phenomenon that can significantly affect thyroid function test results.
• Discontinuation of biotin led to normalization of thyroid function tests and facilitated appropriate levothyroxine dose optimization.

Implications:

• Clinicians should consider biotin interference when encountering unexpected thyroid function test results, especially in patients on high-dose biotin.
• Awareness of biotin's potential to interfere with laboratory assays is critical for accurate diagnosis and treatment.
• Laboratories should identify and validate assays susceptible to biotin interference and implement strategies to mitigate this artifact.