SUN-309 - Spurious Thyroid Function Abnormalities Due to Supplement Use: The Need for Thorough Medication Reconciliation in Clinical Practice

Introduction:
Biotin supplementation use is common due to its well-known benefits for hair, skin, and nail health. However, high-dose biotin can interfere with immunoassays used in thyroid function testing, leading to misleading abnormal biochemical panels that may mimic the true thyroid disease.

Objective:
To highlight the importance of recognizing biotin interference as a cause of discordant thyroid function tests and to highlight the role of a detailed medication and supplement history in clinical evaluation of any hormonal disease.

Case Presentation:
A 42-year-old woman was referred for evaluation of persistently abnormal thyroid function tests over a 2–3 year period. She was asymptomatic for hyperthyroidism, denied weight loss, heat intolerance, palpitations, gastrointestinal symptoms, irregular cycle or dermatologic changes. She was reporting only mild fatigue, difficulty losing weight. There was no personal or family history of thyroid disease.

Her past medical history was unremarkable, and she was not taking any prescription medications. She also had a normal thyroid ultrasound demonstrating a homogeneous gland with normal vascularity, and a radioactive iodine uptake scan showing normal uptake (8% at 6 hours and 16% at 24 hours).

Serial laboratory results revealed persistent suppressed TSH: < 0.001 mIU/L (normal: 0.4–4.0/5.0 mIU/L) free T4: 2.9-3.2 ng/dL (normal: 0.8–1.8 ng/dL) total T3: 270-350 ng/dL (elevated; normal < 200 ng/dL), thyroid peroxidase antibodies (TPOAb): 37 IU/mL (slightly elevated; normal < 35 IU/mL), however thyroglobulin antibodies (TgAb) and TSH receptor antibodies (TRAb/TSI) are negative

Given the significant discordance between clinical findings and laboratory results, further questioning revealed that the patient is also taking an over-the-counter collagen supplement containing 5000 mcg of biotin for years. Biotin interference was suspected. The plan was to discontinue the collagen and repeat thyroid function tests after one week, and the repeated panel showed complete normalization of TSH, free T4, and total T3.

Conclusion:
Detailed history-taking and clear anamnesis and direct patient communication can prevent unnecessary extensive workups.

With the widespread availability and increasing global use of over-the-counter supplements, clinicians should routinely inquire about non-prescription products when evaluating abnormal laboratory results, especially in cases of discordant clinical and biochemical findings.

Although the use of these supplements, like biotin and collagen is safe, abnormal laboratory findings may occur, therefore those supplements should be discontinued one week in advance of blood work if there is discondinance.

Key words: biotin interference, spurious hyperthyroidism, over-the-counter supplements, laboratory artifact, clear anamnesis

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