Thyroglobulin is synthesized in the thyrocytes of the thyroid gland and secreted into the lumen of the thyroid follicles. Synthesis and secretion of thyroglobulin is controlled by TSH. Thyroglobulin is an early marker for metastasis of differentiated carcinoma of the thyroid gland following complete thyroidectomy. Therefore, this test is performed in order to detect recurrent thyroid cancer and to follow the response to treatment in metastatic thyroid cancer. Thyroglobulin testing is also occasionally ordered to help determine the cause of hyperthyroidism and to monitor the effectiveness of treatment for conditions such as Graves disease. HIGHLY elevated thyroglobulin values at the end of a thyrostatic therapy are indicative for an early recidivation. Elevated thyroglobulin serum concentrations have also been reported in various thyroid diseases, such as hyperthyroidism, non-toxic goiter, thyroiditis, and differenciated thyroid carcinoma. See also, Thyroxine (T4), Free, Serum; and Thyroid Stimulating Hormone (TSH), Serum