Clinical significance of elevated labeled TSH binding (LTB) activity in sera of patients with Graves' disease and other thyroid disorders.

Labeled TSH binding (LTB) of individual serum samples was monitored simultaneously using the thyrotropin binding inhibitor immunoglobulin (TBII) assay. In 643 TBII determinations, 86 sera (13.4%) showed elevated LTB. The incidence of elevated LTB in active Graves' patients (17.5%) was much higher than that of inactive Graves' patients (6.7%). After TBII activities were corrected by LTB, 79% of the active Graves' patients who had negative raw TBII were found to be positive. In patients with untreated active Graves' disease, the detectability of TBII increased from 85% to 91% after LTB correction, while those in inactive Graves' and other thyroid disorders did not increase so much (1.6 and 0%, respectively). Further, most of elevated LTB seen in other thyroid disorders were found to be different from those in Graves' disease by heat stability experiment. Serial observations of LTB and TBII in 24 Graves' patients showed 2 patterns. Parallel alterations were observed in 13 patients and reciprocal alterations in 11 patients. Patients showing parallel alteration had smaller goiter and were more sensitive to antithyroid drugs than those showing the latter pattern.