The Thyroglobulin (Tg) test is a vital tumor marker used for long-term monitoring after thyroid cancer treatment. It is not a screening test for the general public. Thyroglobulin is a protein made only by thyroid cells. After a thyroid is removed, this level should drop to near zero. This test is the gold standard for your follow-up care, as a rising level can be the earliest, most sensitive sign of a cancer recurrence. A simple blood draw provides your oncology team with the critical, actionable data needed to manage your health and ensure your long-term well-being.