SUN-381 Suspected Thyroid Hormone Binding Protein Abnormalities: Importance Of Clinical Recognition And Assessment

Abstract Disclosure: D. Hamadi: None. A. Algeciras-Schimnich: None. M. Stan: None. Background: Thyroid hormone-binding proteins (TBPs)—thyroxine-binding globulin (TBG), transthyretin, and albumin—play a critical role in transporting thyroid hormones in the bloodstream. Rare genetic alterations in these proteins can lead to discordant thyroid function test (TFT) results, potentially mimicking thyroid dysfunction despite a clinically euthyroid state. This study retrospectively evaluates the clinical scenarios that warrant TBP testing. Methods: Data was extracted from the electronic medical record (EMR) at the Mayo Clinic in Rochester, MN. The study included patients who had Thyroid-binding protein electrophoresis (TBPE) ordered between 2016 to 2023. Results: A total of 138 patients were included (53% female; median age: 58 years) of which 42% had TBP abnormalities. TBP testing was frequently ordered by endocrinology (33%), followed by cardiology (9%) and family medicine (7%). Discrepancies between thyroid-stimulating hormone (TSH) and total T4 (TT4) were identified in 41 patients of which 75% had abnormal TBP. Among these, eleven were diagnosed with familial dysalbuminemic hyperthyroxinemia (FDH), including one with a known family history. Additionally, five patients were diagnosed with thyroid hormone resistance—one of whom had previously been misdiagnosed with Graves’ disease. Three patients were found to have TSH-secreting tumors, and three were receiving infusion therapy with patisiran with resulting TBP abnormalities. The remaining cases involved binding protein abnormalities, most commonly presenting as elevated TBG. Conclusion: This study identified varied clinical utilization for TBP testing, from very appropriate indications to cases of doubtful clinical utility. TBP abnormalities were clinically meaningful in 22% of cases, supporting the utility of testing in select scenarios. Specifically, TBP testing should be reserved for situations with a clear discrepancy between clinical presentation and TFT results—particularly discordant TSH and total T4 levels. In such contexts, TBP assessment is valuable in preventing misdiagnoses and avoiding unnecessary treatments, especially since individuals with TBP mutations are typically clinically euthyroid. Presentation: Sunday, July 13, 2025