Effect of Therapy on Serum Thyroglobulin Levels in Patients with Graves’ Disease*

Forty-one patients with hyperthyroidism secondary to Graves’ disease (n=34), toxic adenoma (n=5), or multinodular toxic goiter (n=2) were studied. The 34 patients with Graves 's disease were followed for an extended period of time before, during, and after various forms of therapy. All hyperthyroid patients had elevated serum thyroglobulin (HTg) levels before therapy, regardless of cause. Ten patients with euthyroid Graves' disease had normal serum HTg levels ranging from 2.7-13.5 ng/ml. Patients with hyperthyroidism due to Graves’ disease who underwent a subtotal thyroidectomy (n=8) had immediate postoperative increases in serum HTg levels, followed by a rapid fall towards the normal range. Patients who were treated with 131I (n=3) had a rise in serum HTg levels reaching a peak between 24 h to 30 days after radioisotope administration. All patients who underwent successful ablative herapy had significantly lower serum HTg levels after therapy. Of the 24 patients treated with long termantithyroid medication (22 treated with propylthiouracil and 2 with methimazole), some showed moderatechanges from their pretrseatment serum HTg levels during the course of therapy. Nineteen patients completed antithyroid drug treatment; 11 of these patients remained euthryoid during a mean observation period of 37.9 months. The mean serum HTg concentration for this group during the last 3 months of antithyroid drug therapy was 43.0 ± 8.0 (SEM) ng/ml. This was significantly different (P < 0.005) from the value of 229 ± 51.0 (SEM) ng/ml in 8 patients who experienced an exacerbation of their hyperthyroidism after discontinuing antithyroid medication. Serum T3 levels in excess of 500 ng/dl before antithyroid drug therapy were seen in most subjects who exacerbated after discontinuation of their drug therapy. Our tentative conclusion from the present data is that long term antithyroid therapy is likely to be followed by an exacerbation of hyperthyroidism in patients who have high levels of HTg and of T3 before therapy, and is likely to be followed by a remission of hyperthyroidism in patients whose HTg falls to low levels during the course of therapy.