Differences between changes in serum thyrotropin-binding inhibitory antibodies and thyroid-stimulating antibodies in the course of antithyroid drug therapy for Graves' disease

There has recently been controversy regarding whether the measurement of th yrotropin-binding inhibitory antibodies (TBIAb) is useful in the management of Graves' disease. Another method of assessing Graves' disease by measuri ng adenylate cyclase activity in thyroid cells, known as thyroid-stimulatin g antibodies (TSAb), differs from TBIAb not only in terms of assay but also in immunoglobulin type according to recent studies. In this study, the con centrations of TBIAb and TSAb were compared in serial serum samples collect ed from 29 patients with Graves' hyperthyroidism during 12 months of antith yroid drug therapy. Before therapy, there was a correlation between TBIAb a nd TSAb (r = 0.59). The radioactive iodine uptake (RAIU) was not significan tly correlated with either TBIAb or TSAb (r = 0.20 and r = 0.29, respective ly), and the serum free thyroxine (FT4) concentration was also not signific antly correlated with either TBIAb or TSAb (r = 0.06 and r = 0.22, respecti vely). In patients with Graves' ophthalmopathy, TSAb levels were higher tha n in patients without ophthalmopathy (1015% +/- 851% vs. 456% +/- 323%, p < 0.01), but the TBIAb levels were not significantly different. After antith yroid treatment, TBIAb did not decrease significantly (from 42.1% +/- 20.8% to 20.5% +/- 19.5%, P = 0.23). On the other hand, TSAb was significantly d ecreased after 12 months of treatment (from 649% +/- 611% to 294% +/- 205%, p < 0.05). These findings indicate that TBIAb and TSAb are not identical, and that TSAb has a closer relationship to thyroid function than TBIAb. In the clinical setting, determination of the serum TSAb level may provide a m ore accurate index of the thyroid status in Graves' disease patients receiv ing antithyroid therapy.