THU670 Serum TSI Concentration In Patients With Graves’ Disease Undergoing Maintenance-dose Of Antithyroid Drug (ATD) And Its Relationship With Disease Relapse After ATD Withdrawal

Disclosure: P.V. Nguyen: None. K.T. Nguyen: None. Background: Graves' disease (GD) is an autoimmune disorder in which thyroid-stimulating immunoglobulin (TSI) plays a key role in its pathogenesis. TSI assays have been recently optimized in their accuracy, and the procedure has also been simplified, which can potentially replace TRAb measured by conventional TSH-binding inhibitory immunoglobulins (TBII) assays in routine clinical practice. Objectives: Our objective was to study the serum TSI concentration in patients with Graves’ disease undergoing maintenance-dose ATD. We also aimed to assess the predictive value of TSI immunoassay, as well as the clinical signs and thyroid function tests in predicting Graves’ disease relapse following ATD discontinuation. Finally, follow-up would be continued to check for relapse or long term euthyroid status. Methods: Retrospective follow-up study of 352 patients with hyperthyroidism due to GD, treated at the endocrine outpatient clinic of Medic Medical Center, Ho Chi Minh City from January 2000 to April 2021. TSI was measured several times during the course of treatment when planning to stop the medication (at the discretion of the attending physician). ATD withdrawal would be considered when the patients achieved clinical euthyroidism with normal FT4 tests for at least 3 months with minimal dose of ATD. The decision to withdraw ATD was also based on TSI concentration, as well as the goiter’s characteristics and parenchymal vascularity observed via thyroid Doppler ultrasound. Results: The median TSI concentration of patients with GD undergoing maintenance-dose ATD was 1.45 IU/L (normal range