The relationships between serum T3 index, thyroid volume, and thyroid stimulating, TSH receptor binding and thyroid growth stimulating antibodies in untreated Graves' disease.

This study represents an international double-blind collaborative study of abnormal immunoglobulin activity in untreated Graves' disease. Laboratories in two countries participated in a comparison of thyrotrophin binding inhibiting (TBII), thyroid stimulating (TSAb), and growth stimulating (TGI) immunoglobulins with clinical data, including ultrasonically measured thyroid size. The correlation between TGI and thyroid volume (n = 25, Rs = 0.54, P less than 0.05) and the fact that 9 of 10 patients with high range TGI values had large goitres establish the relationship between TGI and goitre, confirming that the in-vitro activity of these antibodies is related to an in-vivo action. In addition, both TBII and TSAb correlated with serum free T3 indices (TBII: n = 60, Rs = 0.46, P less than 0.001, and TSAb: n = 60, Rs = 0.64, P less than 0.001). Moreover, both TBII and TSAb correlated with thyroid volume (TBII: n = 60, Rs = 0.37, P less than 0.01, and TSAb: n = 60, Rs = 0.41, P less than 0.01) suggesting that these antibodies are also important in development of goitre in Graves' disease. Finally, some correlation between the antibodies was observed. TBII correlated with TSAb (n = 60, Rs = 0.47, P less than 0.001), and in the 16 patients with positive TGI results, this activity correlated with TBII (Rs = 0.54, P less than 0.05), but not with TSAb. Also some cases were found with corresponding high range TBII and TGI, while negative for TSAb, suggesting a close relationship between the in-vitro measurement of TSH binding and TGI.