What is the Thyroglobulin (Tg) blood test?
A thyroglobulin test is a blood test that measures the amount of thyroglobulin, a protein that stores thyroid hormone, in your blood. Thyroid cells are the only cells in your body that make thyroglobulin. So if thyroglobulin shows up in your blood test, then you know that normal thyroid cells or thyroid cancer cells are present somewhere in your body. Since thyroglobulin is made in the normal thyroid, it cannot be used to diagnose thyroid cancer. However, after surgery to remove the thyroid and radioactive iodine therapy to destroy any residual thyroid cells, the serum thyroglobulin should be nearly zero in cured patients. A detectable or rising serum Tg after initial therapy may indicate persistent thyroid cancer.
