Significance of Thyroid-Stimulating Immunoglobulin and Thyrotropin Receptor Antibody in Graves Disease

Abstract Context Thyroid-stimulating immunoglobulin (TSI) and thyrotropin receptor antibody (TRAb) are specific biomarkers for Graves disease (GD), but their clinical characteristics are not fully understood. Objective To clarify the clinical features and prognostic significance of TSI and TRAb in patients with GD. Methods We conducted a retrospective data analysis and a follow-up study. Medical records of patients newly diagnosed with GD were examined. TSI and TRAb correlations were assessed using Passing-Bablok regression and Bland-Altman plot. Patients were categorized into unresolved (Group A) and resolved (Group B) hyperthyroidism based on thyroid function after 1 month of therapy. The relationship between thyroid function and changes in TRAb and TSI was analyzed. Logistic regression identified relapse risk factors, including TSI levels at antithyroid drugs (ATDs) withdrawal in the follow-up study. Results Data from 957 patients (762 female and 195 male) revealed a strong correlation between TRAb and TSI (r = 0.873, P < .001). Compared to group B, group A showed minimal antibody decline (100% [interquartile range (IQR) 87.91%-115.1%] and 100% [IQR 85.03%-118.3%], respectively). Among 206 patients followed for over 12 months after ATD discontinuation, the relapse rate was 41.26%. Relapse was more frequent in patients with positive TSI (54.84% vs 35.42%, P < .05). Positive TSI levels at withdrawal, past history of GD, age, and mild thyroid-associated ophthalmopathy were independent relapse predictors. Conclusion TSI and TRAb are strongly correlated in GD, with slow antibody decline linked to unresolved hyperthyroidism. Discontinuing ATDs may be considered when both TSI and TRAb are negative.