Thyrotropin receptor antibodies measured by second-generation assay are highly specific for Graves’ disease and correlate with serum thyrotropin levels in patients with Graves’ disease inremission and during maintenance therapy

Abstract

We compared conventional first-generation thyrotropin receptor antibodies（F-TRAb）and second-generation TRAb （S-TRAb, DYNOtest） in sera. Subjects were 167 cases of Graves’ disease, 5 cases of painless thyroiditis, 8 cases of subacute thyroiditis, 37 cases of chronic thyroiditis, 19 cases of miscellaneous thyroid diseases, 36 cases of Type 1 diabetes mellitus, and 12 cases of other diseases. The latter 3 groups were all negative for thyroid autoantibodies. S-TRAb was completely negative in diseases other than Graves’disease except in 3 cases （8％） of chronic thyroiditis. In patients with Graves’ disease overall, S-TRAb was positive in 102 cases （61％） and F-TRAb was positive in 72 cases （43％）; a positive correlation between S-TRAb and F-TRAb levels was noted. Fourteen cases of untreated Graves’ disease were positive with both methods of measurement in all cases. In 52 cases of Graves’ disease in remission and during maintenance therapy, F-TRAb was positive in only 1 case（ 2％）; S-TRAb was positive in 12 cases（ 23％）. Comparison with these 52 cases - 12 cases that were S-TRAb positive and 40 that were negative - indicated that in positive cases serum thyrotropin levels were significantly lower and serum free thyroxine significantly higher. In these 52 cases, a negative correlation between serum thyrotropin and S-TRAb levels was noted in addition to a negative correlation between serum thyrotropin and free thyroxine levels. In conclusion, S-TRAb is highly specific for Graves’disease except a few cases of chronic thyroiditis. In patients with Graves’ disease in remission and during maintenance therapy, S-TRAb-positive cases are often noted in F-TRAb-negative cases. Since these S-TRAb-positive cases displayed a lower thyrotropin level and a higher free thyroxine level and there was a negative correlation between serum thyrotropin and S-TRAb levels, S-TRAb positivity may reflect minimal disease activity. Further analysis is necessary to examine a relationship between S-TRAb positivity and recurrence of Graves’disease after discontinuation of an antithyroid drug.departmental bulletin pape