Age moderates the associations between TRAbs, free T3, and outcomes of Graves's disease patients with radioactive iodine treatment.

OBJECTIVE This study aimed to explore whether age moderates the associations between TSH-receptor antibodies (TRAbs) with thyroid hormones and remission in patients with Graves' disease (GD) who undergo radioactive iodine (RAI) treatment. DESIGN A single-centre retrospective study. PATIENTS A total of 435 eligible consecutive patients diagnosed with GD, treated with RAI therapy were included. METHODS TRAbs and thyroid hormones before RAI were recorded. Pearson's correlation, t-tests, and analysis of covariance, were conducted to identify the association between TRAbs, thyroid hormones, and remission. Moderation analyses were conducted to test age as a moderator. RESULTS Overall, 75.4% of patients achieved remission with a single dose of iodine-131. TRAbs levels before RAI were positively correlated with the circulating thyroid hormones (ps<0.001). Age moderated the association between TRAbs and free T3 (FT3) (p=0.01), but did not moderate the association between TRAbs and free T4 (FT4) (p=0.07). TRAbs levels before RAI only significantly predicted remission status in young patients (p=0.03), but not in middle-aged (p=0.36) or older patients (p=0.74), after adjusting for covariates. When age was included as a continuous variable, moderation analyses revealed that the association between TRAbs and remission status was stronger in younger patients (p=0.03). CONCLUSIONS The majority of Graves' disease patients experienced a long-term remission following a single dose of iodine-131. Associations between TRAbs, FT3, and remission are moderated by age. TRAbs value prior to RAI is a significant predictor of remission in younger patients, but not in middle-aged or older patients.