A receptor assay for TSH receptor antibodies is described in which unextracted serum, detergent solubilised TSH receptors and 125I-labelled TSH are used. The assay was rapid and reproducible with coefficients of inter-assay variation of 12.3%, 2.1 and 2.6% at mean inhibition of TSH binding values of 11, 53, and 79 respectively. Assay sensitivity could be increased by reducing the volume of receptors used but some increase in the scatter of values obtained with individual normal sera was also observed. Comparison of human and porcine TSH receptor preparations indicated that porcine tissue gave greater sensitivity. Analysis of different groups of patients and normal subjects (n = 21) showed the absence of detectable TSH receptor antibody activity in 16 patients with rheumatoid arthritis, 10 with multinodular goitre and 12 with Hashimoto's disease. However the antibody was readily detectable in 28 out of 28 Graves' patients (treated and untreated) who were hyperthyroid at the time of assay.

Improved receptor and bioassays have been used to compare TSH receptor binding and thyroid stimulating activities in unextracted sera from 110 patients with Graves' disease. The two parameters showed a significant correlation (r = 0.65; P less than 0.001) although there were some clear discrepancies. Dose-response studies in 17 sera showed that both receptor binding and thyroid stimulating responses always increased with increasing doses of serum. In patients who were in relapse or remission following antithyroid drug treatment, the results of both bio- and receptor assays correlated well with disease activity with only one clear discrepancy which could have been attributable to the coexistence of autoimmune stimulation and destruction of the thyroid.