Serum thyroglobulin in normal subjects and patients with hyperthyroidism due to Graves' disease: effects of T3, iodide, 131I and antithyroid drugs.

Abstract

SUMMARYA sensitive, reproducible radioimmunoassay for thyroglobulin (Tg) in unextracted human serum is described. The mean (± SD) serum thyroglobulin concentration in ninety‐three normal subjects was 8±8 ± 5±1 ng/ml. The mean serum Tg concentration in forty‐seven patients with hyperthyroidism due to Graves’disease was 162 ± 145 ng/ml, and in nine patients with subacute thyroiditis 140 ± 75 ng/ml. The administration of T3, 75 /μg daily for 3 weeks to normal subjects, produced parallel and significant decreases in both serum Tg and T4 concentrations. Administration of iodide to normal subjects for 13 days resulted in significant increases in serum Tg concentrations, associated with increases in serum TSH and decreases in serum T4 concentrations. In patients with hyperthyroidism due to Graves’disease, iodide administration had no effect on serum Tg concentrations in five of six patients studied, though all had a reduction in serum T4 and T3. Administration of radioactive iodine, with or without iodide, to hyperthyroid patients resulted in acute increases in serum Tg concentrations in all patients. In patients with hyperthyroidism due to Graves’disease treated with antithyroid drugs, serum Tg concentrations were initially lower (mean 109 ng/ml) and declined to or towards normal during therapy in those who subsequently achieved remission. Initial serum Tg concentrations were higher (mean 207 ng/ml) and serum Tg concentrations did not change in the patients who developed recurrent hyperthyroidism when antithyroid drug therapy was decreased or discontinued. These data suggest that: (1) Tg release by the thyroid is normally under TSH control; (2) iodide inhibits thyroidal T4 and T3 release without affecting Tg secretion; (3) thyroidal injury results in marked increases in serum Tg concentrations; and (4) initial and/or serial Tg determinations may be useful in predicting remission in patients with hyperthyroidism due to Graves’disease treated with antithyroid drugs.