Clinical Usefulness of the Second Generation TSH-Binding Inhibitory Immunoglobulin Assay Using Recombinant Human TSH Receptor in Patients with Graves' Disease

Abstract

Background and Aim: Detection of TSH receptor antibody in patients with Graves' disease (GD) has been widely used in clinical practice. This has been performed mostly by commercial radio-receptor assays that measure TSH-binding inhibitory immunoglobulin (TBII) with using porcine TSH receptor as the ligand. To increase the sensitivity of the assay, many research groups have tried to replace the porcine source of TSH receptor with recombinant human TSH receptor. In this study we evaluated the clinical usefulness of the second generation TBII assay, which uses recombinant human TSH receptor, for making the diagnosis of GD, as compared to the conventional TBII assay. Materials and Methods: We obtained sera from 76 patients with newly diagnosed or relapsing GD without or with less than 4 weeks of antithyroid drugs, and 54 patients with Hashimoto's thyroiditis who had not received thyroid hormone treatment or quit thyroid hormone more than 3 months before. TBII was measured by using both the conventional porcine TBII assay (pTBII) and the human recombinant TBII assay (hTBII). TBII was also measured in the sera from 66 healthy controls. Results: The cut-off values of the pTBII and hTBII assay were defined as two geometric standard deviations from the geometric mean of the values in healthy controls, and these values were 10.8 IU/L and 1.0 IU/L, respectively. The sensitivity was 62% (47/76) for pTB II, as compared to 100% (76/76) for the hTBII, for diagnosing GD. Of the 54 patients with Hashimoto's thyroiditis, 3 (5.6%) and 7 (13.0%) patients had positive pTBII and positive hTBII, respectively. Conclusions: These data showed that the hTBII assay was a comparable method in terms of the sensitivity for the diagnosis of GD, as compared to the pTBII assay. It can be suggested that this new hTBII assay, rather than the pTBII assay, should be more widely used as the first line diagnostic test for GD. (J Korean Endocr Soc 23:179~185, 2008)