Clinical utility of TSH receptor antibody levels in Graves' orbitopathy: a comparison of two TSH receptor antibody immunoassays.

Introduction: Thyroid stimulating hormone (TSH) receptor antibodies (TRAB) play a role in the development of Graves' orbitopathy (GO), and measurements of the TRAB level may be helpful in monitoring GO treatment. Aim of the study: To assess the correlation of TRAB levels measured with two different assays: third-generation TRAB assay (TRAB Cobas) and novel Immulite assay (TRAB Immulite), in patients with moderate-to-severe GO treated with intravenous glucocorticoid pulse therapy (ivGCs). Material and methods: Forty patients with active, moderate-to-severe GO underwent clinical and laboratory evaluation before, in the middle, and after ivGCs therapy. The correlation of TRAB levels with GO signs was evaluated. Laboratory and clinical findings were compared according to the response to ivGCs. TRAB concentration was measured with Immulite TSI assay and with Elecsys IMA. Results: All patients were TRAB positive in both assays at the beginning of the treatment. The decrease of both TRAB Immulite and Cobas levels in serum during ivGCs was statistically significant. We observed strong correlation between both TRAB levels before and after ivGCs. There was no statistically significant difference in antibody levels between patients with good response and no response to the treatment. We did not find any correlation between antibody levels and GO features before the therapy, but measurements during ivGCs showed comparable correlation of both TRAB levels with GO activity. Conclusions: We found similarity between Immulite assay and third-generation TRAB assay in the assessment of patients with GO treated with ivGCs. Both TRAB levels showed comparable correlation with GO activity during ivGCs therapy.