Assays for thyrotropin-receptor binding and thyroid-stimulating antibodies in sera from patients with Graves' disease

We compared the activities of thyroid-stimulating antibodies (TSAb) measured in cultures of human thyrocytes and the values for thyrotropin-receptor antibodies (TRAb) as measured with a commercial kit based on use of radiolabeled receptors. Sera were obtained from patients with Graves' disease before, during, and after therapy with carbimazole (1-methyl-2-thio-3-carbethoxyimidazole). We found a significant correlation between the measurements of these two antibodies in patients: before treatment (r = 0.74, p less than 0.01, n = 44), after three months of treatment (r = 0.76, p less than 0.01, n = 21), and during relapse after the drug was discontinued (r = 0.64, p less than 0.01, n = 19). In all three situations, our TSAb technique was more sensitive than the TRAb method. We conclude that, even though the TRAb technique is simpler and quicker, this commercial kit is too insensitive to replace measurement of TSAb in fresh human thyrocyte cultures for management of drug therapy of patients with Graves' disease.