Thyroglobulin

A thyroglobulin test measures the thyroglobulin level in a sample of your blood. Thyroglobulin is a protein made by your thyroid. Your thyroid is a small butterfly-shaped gland located in your neck. It produces hormones that control many activities in your body, including your heart rate and the rate at which you burn calories from food.

A thyroglobulin test is a type of tumor marker test. Tumor markers are substances that are produced by cancer cells and/or by normal cells in response to cancer in your body. Normally, your thyroid releases small amounts of thyroglobulin into your bloodstream. Cells of the common types of thyroid cancer (papillary carcinoma and follicular thyroid cancer) also release thyroglobulin.

The thyroglobulin test is not used to diagnose thyroid cancer because other thyroid conditions that are not cancerous can also affect thyroglobulin levels. But the test is useful thereafter treatment for common thyroid cancers to see if the treatment worked That's because the goal of treatment is to remove all thyroid tissue — both healthy cells and cancer cells. So if the treatment is successful, there should be little or no thyroglobulin in your blood. If thyroglobulin levels stay the same or increase, additional cancer treatment may be required.

Other names: Tg, TGB. thyroglobulin tumor marker

A thyroglobulin test is primarily used to:

• Verify whether thyroid cancer treatment has been successful and guide decisions about additional treatment.
• Predict how your cancer will behave over time
• Check to see if the cancer has returned after successful treatment.

Thyroglobulin tests may also be used to help diagnose hyperthyroidism and hypothyroidism, which are common thyroid conditions that are not cancerous.

You may need a thyroglobulin test before starting treatment for thyroid cancer. Your health care provider will compare these test results to your test results after treatment.

You may also need this test a few weeks after completing thyroid cancer treatment. The test helps to show if there are thyroid cells left in your body. If your treatment has been successful, you may still need to have your thyroglobulin levels tested from time to time to see if the cancer has returned.

You generally do not need special preparations for a thyroglobulin test. But you should avoid taking certain vitamins or supplements, so let your provider know everything you are taking.

There is very little risk in taking a blood test. You may feel a slight pain or bruise where the needle was inserted, but most symptoms go away quickly.

Understanding the results of a thyroglobulin test after treatment can be complicated. What your results mean depends on your medical history, the type of treatment you received, and the results of other tests. So it's best to ask your provider to explain what your test results say about your health.

In general, if you have been tested after treatment for thyroid cancer:

• Very low or no thyroglobulin levels may mean that your cancer treatment has successfully removed all thyroid tissue, including cancer. But you'll still need additional testing over time to be sure.
• Thyroglobulin levels that remain high or increase may mean that:
  • Your treatment did not remove all of the thyroid tissue in your body.
  • You still have thyroid cancer in your body that has grown and may have metastasized.
• Thyroglobulin levels that were low after treatment but then increased may mean that your thyroid cancer has come back after treatment.

Learn more about lab tests, reference ranges, and understanding results.

Laboratories use a variety of methods to measure the amount of thyroglobulin in your blood sample. The test method may affect your results. It is therefore important to do your tests in the same way, and generally in the same laboratory. This allows your provider to compare your results over time. If you have questions about this, talk to your provider.

A thyroglobulin test may not be useful in monitoring the treatment of your thyroid cancer if you have anti-thyroglobulin antibodies in your blood. These antibodies are proteins that your immune system can produce. They attach to thyroglobulin and can cause your thyroglobulin levels to appear lower than they actually are.

Your provider will usually order a thyroid antibody test to determine if the thyroglobulin test will be helpful. If you have thyroglobulin antibodies, further tests will be used to see if your cancer treatment has been effective.

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