The dynamics of serum thyroglobulin elimination from the body after thyroid surgery.

Thyroglobulin (Tg) is a glycoprotein produced exclusively by the thyroid. It can be found in the serum of healthy people as well as of those with various thyroid disorders. Elimination of Tg from the body occurs through the liver. The data on Tg serum half-life in the literature are scarce, and the reported values vary from 6-96 h. The aim of our study was to determine the Tg half-life after surgical removal of the thyroid gland. Knowing the exact half-life of Tg would enable rational timing of sampling serum for determination of Tg after thyroid surgery or chemotherapy and/or irradiation for evaluation of treatment in patients with differentiated thyroid cancer (DTC). In 11 patients (10 females and one male, aged 27-85 years) serum samples were taken 24, 48, 72 and 168 h after a near-total or total thyroidectomy. Serum Tg levels were determined and Tg half-life calculated by the use of a one-compartment kinetic model. Mean Tg half-life was 65.2 h (SEM = 4.3), and Tg levels decrease below 5-10 ng/ml approximately only 25 days after thyroidectomy (7-10 x t1/2). Therefore, earlier determination of Tg cannot be used either for reliable detection of distant metastases or for evaluation of the effect of chemotherapy and/or irradiation.