Thyrotropin displacement activity of serum immunoglobulins from patients with Graves' disease.

A radioreceptor assay for human thyroid stimulators has been employed in various groups of patients. The ability of Ig to displace the labeled TSH from the receptors is referred to as "TSH displacement activity (TDA)." In active Graves' disease, TDA was above normal in 76% of the cases, and in the remaining patients, it was above the 76th percentile, suggesting that thyroid-stimulating Ig (TSIg) may have been present in all cases, but not always demonstrable by this method. Significant TDA was not found in normal persons or in toxic or nontoxic nodular goiters. It was also negative in some patients with "euthyroid ophthalmic Graves' disease." In patients with Graves' disease controlled with antithyroid drugs, positive TDA accurately predicted the recurrence of hyperthyroidism in eight of nine cases from whom the drugs were withdrawn. Thus, TSIg appears to be a prerequisite of the hyperthyroidism of Graves' disease. Moreover, the remission of hyperthyroidism was due to the disappearance of TSIg (immunological remission) in most cases in this small series. Serum TDA may provide a means of detecting immunological remission. The exophthalmos of Graves' disease does not require thyroid-stimulating Ig.