An improved radioreceptor assay for TSH receptor antibodies.

An improved receptor assay for TSH receptor antibodies is described in which detergent-solubilized TSH receptors and 125I-labelled TSH are used. Normal human serum and immunoglobulin concentrates from normal serum showed little effect on the interaction between labelled TSH and detergent-solubilized receptors whereas immunoglobulin concentrates from some Graves sera caused marked inhibition of TSH binding. Precipitation with polyethylene glycol was the most convenient way of preparing immunoglobulin concentrates and using this technique the assay could be completed in a few hours. The coefficient of inter assay variation at 51% inhibition of labelled TSH binding was 3.7% and analysis of serum samples from patients with Graves' disease (n = 42), Hashimoto's disease (n = 26), multinodular goitre (n = 9), rheumatoid arthritis (n = 10) and normal donors (n = 35) suggested that the assay could detect TSH receptor antibodies in about 80% of patients (treated and untreated) with Graves' disease.