SUN-353 Is It Back: A Case of Elevated Thyroglobulin and Thyroglobulin Antibody After a Diagnosis of Immunodeficiency and Starting Intravenous Immunoglobulin in a Patient with Thyroid Cancer in Remission

Abstract B.I. Zaidan: None. L. Kukova: None. A. Kidwai: None. X. Ning: None. K.M. Munir: None. Background: Thyroglobulin (TG) is a protein produced by the thyroid gland and is used as a tumor marker in the monitoring of thyroid cancer (1). Intravenous immunoglobulin (IVIG) is a concentrated solution of antibodies, typically derived from pooled blood donations to treat various medical conditions, including autoimmune disorders and immunodeficiencies (2,3). We report a case of IVIG interference with TG monitoring in a patient with thyroid cancer in remission. Case description: A 46-year-old female with a history of a 2.5 cm papillary thyroid cancer s/p thyroidectomy and I-131 therapy in 2004 had been in clinical remission since then. TG and TG antibody levels had been suppressed and no evident disease on thyroid ultrasound was noted over the years. More recently, the patient was diagnosed with hypogammaglobinemia in the of setting of recurrent infections. Intravenous immunoglobulin infusions were initiated every 4 weeks. After receiving 5 infusions, a new elevation in thyroglobulin antibody with a peak of 23 IU/ml and thyroglobulin level of 6.2 ng/ml was noted. Levels improved to 8IU/ml and <2.0 ng/ml, respectively, one month after discontinuations of intravenous immunoglobulin. More recently, the level improved to 2.9 IU/ml and <2.0 ng/ml, respectively, four months after discontinuation of intravenous immunoglobulin. Thyroid ultrasound and I-131 whole body imaging revealed no evidence for recurrent disease in the neck or metastases. PET/CT did not show any thyroid related FDG uptake. Conclusion: This case showed elevations of TG and TG antibody after starting IVIG therapy for immunodeficiency. The interference of IVIG with TG assays can potentially confound the interpretation of thyroid cancer monitoring. The exact mechanism by which IVIG interferes with TG measurement is not fully understood, but it is believed to involve the presence of antibodies or other substances in the IVIG preparation that may cross-react with the thyroglobulin assay (3). Providers should be aware of potential elevations in TG and TG antibody in patients with thyroid cancer receiving IVIG. Reference: 1.Ogrin C, Ford BA, Stauffer SL, Krasowski MD, Azar AE. POSITIVE TEST FOR ANTITHYROGLOBULIN ANTIBODIES DUE TO ADMINISTRATION OF IMMUNOGLOBULIN REPLACEMENT THERAPY IN A PATIENT WITH THYROID CANCER. Endocr Pract. 2015;21(8). 2.Uchida Y, Kato D, Adachi K, Toyoda T, Matsukawa N. Passively acquired thyroid autoantibodies from intravenous immunoglobulin in autoimmune encephalitis: Two case reports. Vol. 383, Journal of the Neurological Sciences. 2017. 3.Zia M, Selk K. SUN-625 A False Alarm: Elevated Thyroglobulin Levels in a Patient Receiving Intravenous Immunoglobulin. J Endocr Soc. 2019;3(Supplement_1). Sunday, June 2, 2024