What is Thyroglobulin?

Thyroglobulin is Used as a Tumor Marker

Neck anatomy illustration
Neck anatomy illustration. Getty Images/BSIP/UIG

Thyroglobulin, also known as Tg, is a protein produced in the thyroid that is then converted into the thyroid hormones T3 and T4, which help the body regulate metabolism. Thyroglobulin is made by the follicular cells of the thyroid gland, which is located at the lower-front portion of your neck. It is produced by both normal and cancerous thyroid cells.

If your thyroid gland is removed in a thyroidectomy, you can no longer make thyroglobulin.

This means that its presence can be used as a tumor marker for certain types of papillary thyroid cancer and follicular thyroid cancer. If it is found, it means some thyroid tissue or tumor remains or has come back.

Thyroglobulin is attacked by autoantibodies in some autoimmune disorders, leading to thyroid conditions that can result in either an overactive thyroid (hyperthyroidism) or an underactive thyroid (hypothyroidism).

Diagnostic Testing of Thyroglobulin

It is normal to have a small amount of thyroglobulin detected in the blood stream, but a high concentration can point to various disease conditions, not all of which are due to cancer.

Your doctor may test for thyroglobulin if she suspects an overactive thyroid in disorders such as hyperthyroidism, Graves disease or thyroiditis. If you are being treated with an anti-thyroid medication, she may follow your thyroglobulin levels to see if it is effective or needs adjustment.

Thyroglobulin in Thyroid Cancer - Use as a Tumor Marker

A common reason to test for thyroglobulin is in thyroid cancer. The thyroglobulin test is not used to detect or diagnose cancer in itself, but it is used as a tumor marker after you have been diagnosed by biopsy. If the levels are high before the thyroid is removed, it is probably due to the cancer cells producing the excess.

After the thyroid is removed, levels of thyroglobulin are measured at intervals to ensure it is falling and it should eventually be undetectable.

If your follow-up tests begin to detect thyroglobulin again and the concentration is rising, it may mean the cancer has come back. If there is any remaining active thyroid tissue or tumor that continues to produce thyroglobulin, the doctor may do tests including a radioactive iodine scan, PET or other scans. Further treatment such as surgery, radioactive iodine or radiation may be done to kill the remaining cells.

The thyroglobulin test is a blood test done on a blood sample drawn from a vein. It is then sent to a laboratory for testing and reporting.

Thyroglobulin Antibody Testing

Sometimes the body makes antibodies to thyroglobulin, known as Tg antibodies. These autoantibodies attack thyroglobulin and destroy your thyroid gland. A thyroglobulin antibody test helps to diagnose thyroid problems including Hashimoto's thyroiditis, Graves disease, and autoimmune thyroid disease - both hypothyroid conditions and hyperthyroid conditions.

If it is suspected that you have a thyroid disorder, your doctor will have you take this test. It is a blood test done on blood drawn from your vein and sent to the laboratory.

If there are no thyroglobulin antibodies in your blood, the test results will be negative. A positive test means that thyroglobulin antibodies exist in your blood. This indicates that you may have a problem with your thyroid gland. It may also mean that the test in inaccurate and may need to be repeated. If you are on thyroid hormone medication, it can affect the results of the test.


Thyroglobulin, LabTestsOnline.org, American Association for Clinical Chemistry, February 24, 2015.

Thyroid Antibodies, LabTestsOnline.org, American Association for Clinical Chemistry, February 26, 2016.

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