SAT-314 - Transient Thyroid Index Abnormalities in a Patient Taking Biotin: Signal or Laboratory Noise ?

Transient Thyroid Index Abnormalities in a Patient Taking Biotin: Signal or Laboratory Noise ?

A 34-year-old premenopausal woman with stage II HER2-positive, ER-positive breast cancer diagnosed two years prior presents for routine follow-up with concern of fatigue. She had completed neoadjuvant Pertuzumab-based chemotherapy one year prior, followed by bilateral mastectomy with reconstruction achieving pathologic complete response (ypT0N0), and subsequently radiation. Patient remained on ovarian suppression with leuprolide and an aromatase inhibitor.

At the time of presentation, thyroid testing revealed a markedly suppressed TSH of 0.02 mcIU/mL; reference 0.30 - 4.20) with normal free T3 (3.1 pg/mL) and free T4 (1.34 ng/dL) and no clinical symptoms of thyrotoxicosis. No prior thyroid studies were available. Pituitary axis evaluation was normal, making central hypothyroidism unlikely. Differentials included early thyroid disease, physiologic variation, Jod-Basedow effect from iodinated contrast exposure, analytic error, and assay interference.

Further history revealed daily use of 5,000 mcg biotin supplement, which was held for one week, with repeat testing resulting in normalization of TSH (1.83 mcIU/mL), with persistently normal free T3 (2.19 pg/mL) and free T4 (1.19 ng/dL) on testing, raising suspicion for possible assay interference.

At our institution, thyroid testing uses Roche cobas immunoassays incorporating streptavidin–biotin capture chemistry. Interference typically requires markedly elevated circulating biotin concentrations (>1200 ng/mL for TSH; >20 ng/mL for free T4; >70 ng/mL for free T3). Because isolated TSH suppression without elevation of free thyroid hormones is not a common pattern of biotin interference, analytic variation or transient physiologic suppression cannot be excluded.

This case highlights the importance of interpreting discordant thyroid function tests in the context of assay platform characteristics and supplement exposure history. Isolated TSH suppression on Roche-based assays should be interpreted cautiously when other thyroid indices remain normal, especially in a patient with normal renal function.

Points to be discussed
• Roche cobas thyroid immunoassays use streptavidin-biotin chemistry but typically require very high biotin concentrations to affect TSH measurements
• Pattern recognition of isolated low TSH with normal FT4/FT3 as possible assay artifact
• Risk of unnecessary endocrine referrals or treatment from false labs
• Importance of medication/supplement reconciliation before interpreting thyroid labs

Future research
• Prevalence of clinically significant thyroid assay interference among supplement users
• Development of biotin-resistant immunoassay platforms
• Standardized screening approaches for supplement-related laboratory interference in oncology and primary care populations

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*