Early changes in thyroid-stimulating antibody activity following radioiodine therapy.

OBJECTIVE The aim of this study was to determine whether or not the titre of thyroid-stimulating hormone receptor antibody with stimulating (TRAb-S) activity changes in patients with Graves' disease (GD) or toxic multinodular goitres (TMNG) 3 months after treatment with sodium iodide ((131)I). SUBJECTS AND METHODS Serum specimens were obtained from 21 hyperthyroid patients (15 with GD and 6 with TMNG) at a median 0.5 months before and 3 months after (131)I treatment using a standard ablative dose of 555 MBq. TRAb-S activity was measured in a sensitive and specific luminescent bioassay employing the lulu cell line and expressed as a stimulation index (SI; normal </=1.5). RESULTS The mean TRAb-S in the GD patients was 2.72 SI (95% CI: 1.51-4.03) 0.5 months before administration of (131)I and 3.98 SI (95% CI: 1.20-6.76) 3 months after administration of (131)I. The difference was not statistically significant at p LT; 0.8. It was not elevated in the TMNG patients before (0.57 SI; 95% CI: 0.41- 0.73) and after (1.00 SI; 95% CI: 0.74-1.26) treatment either. CONCLUSIONS Radioiodine therapy for GD or TMNG did not induce a significant change in TRAb-S activity at 3 months after treatment with (131)I, probably due to effective antithyroid therapy or the timing of samples.