Thyroglobulin

A thyroglobulin test measures the amount of a protein called thyroglobulin (Tg) in a sample of your blood. Your thyroid (a small, butterfly-shaped gland in your neck) makes thyroglobulin along with many other important hormones. Together, these hormones control bodily activities such as your heart rate and how fast you burn calories from food.

Normally, your thyroid releases small amounts of thyroglobulin into your bloodstream. However, various conditions that affect the thyroid can lead to higher levels of this protein. The most common causes of high thyroglobulin levels are two types of thyroid cancer called papillary carcinoma and follicular thyroid cancer.

In both conditions, cancerous cells produce thyroglobulin. Because of this, thyroglobulin is usually measured as a tumor marker. Tumor markers are substances made by cancer cells and/or by normal cells in response to cancer in your body.

Other conditions can, however, affect your thyroglobulin levels. These include various thyroid diseases such as: Hyperthyroidism, a condition where your thyroid becomes overactive and makes too much thyroglobulin.; Hypothyroidism, a condition where your thyroid becomes underactive and makes too little thyroglobulin.; Thyroiditis, a condition caused by inflammation of the thyroid, which can lead to a temporary rise in thyroglobulin levels.; Because such a wide range of conditions can affect thyroglobulin levels, health care providers don’t use the results from a thyroglobulin test to diagnose cancer.

Why this test is done

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

You may also need this test:

• Four to six weeks after treatment for thyroid cancer to check whether all thyroid tissue has been removed.
• Regularly after successful treatment to make sure cancer hasn’t come back.

If your provider is monitoring a thyroid condition that isn’t cancer, a thyroglobulin test can help evaluate how active your thyroid cells are and how your treatment is working.

How to prepare

You usually don’t need any special preparations for a thyroglobulin test. But you need to avoid taking certain vitamins or supplements so tell your provider about everything you take.

Sample type

Blood

Other names for this test

Tg, TGB, thyroglobulin tumor marker