Thyrotrophin displacement activity of serum immunoglobulins in health and disease

A radioreceptor assay for TSH displacement activity (TDA) was employed as an index of thyroid stimulating immunoglobulins (TSlg) in serum from patients with autoimmune thyroid disease. TDA was less than or equal to 20 in normal subjects (37/37), patients without thyroid disease (36/38), non-toxic goitre (18/19) and toxic nodular goitre (16/17) and was significantly lower in Nepalese subjects with severe endemic goitre. TDA was greater than 20 in 84% of patients with untreated hyperthyroid Graves' disease (70/83), in Hashimoto's thyroiditis (3/17) and following subtotal thyroidectomy (8/14) or 131I therapy (7/11), but was less than or equal to 20 in euthyroid patients treated with carbimazole (58/59) and during spontaneous remission (18/19). Serial TDA measurements during antithyroid drug therapy suggested that carbimazole has a direct effect in reducing TSlg concentration but that TDA is not a useful prognostic indicator of short term relapse or remission.