An improved assay for thyrotropin-binding blocking activity in serum of patients with Graves' disease.

An improved assay for detecting blocking or inhibitory activity on TSH-binding (TBBA) in neat serum of patients with Graves' disease is described. The assay is sensitive, reproducible, simple, and quick. Crude membranes prepared from guinea pig fat (FCM) were used as the source of TSH receptors. One major feature of the assay is the use of small amounts of FCM to increase assay sensitivity. The sensitivity of the assay was found to be inversely proportional to the amount of FCM used. Using a quantity of 10-20 micrograms crude FCM achieved a satisfactory balance between assay sensitivity and accuracy. The assay employs two sequential one-hour incubations at room temperature, first incubating the FCM with the serum sample, followed by removal of excess sample and washing, and then incubating the exposed FCM with 125I-TSH for quantitative determination of specific TSH binding. The assay is recommended as a standard method for measurement of blocking activity in serum of specific TSH binding. Seventy-four percent of the patients with Graves' disease showed positive blocking activity while all normal individuals and patients with Hashimoto's thyroiditis and with nonautoimmune thyroid disorders were negative.