Radioimmunologic assay for antithyroglobulin antibodies

A double-antibody radioimmunologic assay for antithyroglobulin antibodies (RATA) in serum is described. The assay employs human thyroglobulin labeled in vitro. The reaction product of antithyroglobulin antibodies and labeled human thyroglobulin is measured after precipitation with rabbit antihuman gamma-globulin serum. This test has a high degree of positivity in autoimmune thyroid disorders. In chronic lymphocytic thyroiditis, 100 per cent of sera from patients with surgically proved disease were positive and 83.8 per cent of those in whom this disease was clinically suspected were positive. In Graves' disease, 87.5 per cent of untreated patients' sera and 57.7 per cent of treated patients' sera were positive. In primary hypothyroidism, 94.4 per cent of patients' sera were positive. The sera from many patients with autoimmune thyroid disorders which were negative or had low titers to the commonly used tanned red cell agglutination test (TRCA) were positive with the RATA test. Four per cent of sera from normal control subjects, 15 per cent of sera from patients with other autoimmune disorders, and 8 per cent of sera from patients with thyroid disorders not considered to be of an autoimmune etiology were positive to the RATA. The RATA is simple and quantitative with sensitivity and specificity equal to or exceeding present tests for circulating antithyroglobulin antibodies.