Age moderates the associations between TRAbs, free T3 and outcomes of Graves’ 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 and treated with RAI therapy were included. METHODS: TRAbs and thyroid hormones prior to RAI were recorded. Pearson's correlation, t tests and analysis of covariance were conducted to identify the associations between TRAbs, thyroid hormones and remission. Moderation analyses were conducted to test age as a moderator. RESULTS: Overall, 75.4% of the patients achieved remission with a single dose of iodine‐131. TRAb 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 = .01), but did not moderate the association between TRAbs and free T4 (FT4) (P = .07). TRAb levels before RAI only significantly predicted remission status in young patients (P = .03), but not in middle‐aged (P = .36) or older patients (P = .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 = .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. TRAb level prior to RAI is a significant remission in younger patients, but not in middle‐aged or older patients.