TSH-receptor antibody measurement in patients with various thyrotoxicosis and Hashimoto's thyroiditis: A comparison of two two-step assays, coated plate ELISA using porcine TSH-receptor and coated tube radioassay using human recombinant TSH-receptor

The aim of this study was to compare two two-step assays, a new coated plate (CP) ELISA assay (TRAb ELISA) using purified porcine TSH-receptors (pTSH-R) and a coated tube assay (CT) using recombinant human TSH-receptors (hTSH-R) (DYNOR test TRAK human). The same serum samples were used for the determination by both assays in patients with 100 untreated Graves' disease (GD), 30 silent thyroiditis (ST), 10 subacute thyroiditis (SAT) and 87 Hashimoto's thyroiditis (HT). In sera from patients with untreated GD, pTBII and hTBII were positive in nearly all cases except the same one, whereas the thirty sera from the ST had positive values of pTBII in one case and of hTBII in 4 cases. In the one ST case of both pTBII and hTBII positive, hyperthyroidism developed following ST, although the remaining ST cases including the three hTBII-positive cases were not followed by hyperthyroidism after ST attack. A positive value of hTBII was observed in one of 10 patients with SAT, whereas none of them was pTBII positive. In the 87 patients with HT, positive values of pTBII were recognized in 9 patients, whereas hTBII is positive in 10 patients. Serum TSAb and TSBAb activities were analyzed in the hTBII positive 7 patients. As a result, TSAb was all positive except one and TSBAb positive in 4 cases. Since there is no significant difference in the sensitivity and specificity between the two assays in the differentiation of thyrotoxicosis as well as the frequency of finding positive values in patients with HT, it is reasonable to conclude that the clear advantage of sensitivity for clinical application in the new CP and CT assays may be derived from the coated plate or coated tube assay itself, which probably excludes the effect of anti-TSH antibodies and HAMA, and is unrelated to the use of human or porcine TSH-receptors.