Optimization and clinical assessment of a radioreceptor assay for thyrotropin-binding inhibitor immunoglobulins.

We tried to improve the sensitivity of a radioreceptor assay for thyrotropin-binding inhibitor immunoglobulins (TBII) by modifying assay conditions. About a twofold increase in sensitivity without a loss of reproducibility was obtained by prolonging the incubation of the receptors with test serum from 15 to 120 min before the addition of 125I-labeled thyrotropin. In 20 untreated, 49 treated patients with Graves' disease and 19 patients with euthyroid Graves' disease, TBII activities obtained using 120 min preincubation were significantly higher than those obtained using 15 min preincubation (p less than 0.005). No significant increase in TBII activities was observed in the presence of sera from patients with primary hypothyroidism (n = 17), simple goiter (n = 7), adenomatous goiter (n = 11), thyroid adenoma (n = 11) or cancer (n = 12). TBII were detectable in 15 (47%) of 32 triiodothyronine-nonsuppressible Graves' patients who were receiving maintenance antithyroid drug therapy using 120 min preincubation, while they were positive in only 6 patients (19%) using 15 min preincubation. The assay using a longer preincubation period was found to be sensitive, specific and useful for diagnosis and follow-up of Graves' disease.