What is a thyroglobulin test?
This test measures the level of thyroglobulin in your blood. Thyroglobulin is a protein made by cells in the thyroid. The thyroid is a small, butterfly-shaped gland located near the throat. A thyroglobulin test is mostly used as a tumour marker test to help guide thyroid cancer treatment.
Tumor markers, sometimes called cancer markers, are substances made by cancer cells or by normal cells in response to cancer in the body. Thyroglobulin is made by both normal and cancerous thyroid cells.
The main goal of thyroid cancer treatment is to get rid of all thyroid cells. It usually involves removing the thyroid gland through surgery, followed by therapy with radioactive iodine (radioiodine). Radioiodine is a medicine used to destroy any thyroid cells that are left after surgery. It is most often given as a liquid or in a capsule.
After treatment, there should be little to no thyroglobulin in the blood. Measuring thyroglobulin levels can show whether thyroid cancer cells are still in the body after treatment.
Other names: Tg, TGB. thyroglobulin tumor marker
What is it used for?
A thyroglobulin test is mostly used to:
- See if thyroid cancer treatment was successful. If thyroglobulin levels stay the same or increase after treatment, it may mean there are still thyroid cancer cells in the body. If thyroglobulin levels decrease or disappear after treatment, it may mean there are no normal or cancerous thyroid cells left in the body.
- See if cancer has returned after successful treatment.
A healthy thyroid will make thyroglobulin. So a thyroglobulin test is not used to diagnose thyroid cancer.
Why do I need a thyroglobulin test?
You will probably need this test after you’ve been treated for thyroid cancer. Your health care provider may test you regularly to see if any thyroid cells remain after treatment. You may be tested every few weeks or months, beginning shortly after treatment ends. After that, you would be tested less often.
What happens during a thyroglobulin test?
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for the test?
You usually don’t need any special preparations for a thyroglobulin test. But you may be asked to avoid taking certain vitamins or supplements. Your health care provider will let you know if you need to avoid these and/or take any other special steps.
Are there any risks to the test?
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results mean?
You will probably be tested several times, beginning shortly after treatment ends, then every so often over time. Your results may show that:
- Your thyroglobulin levels are high and/or have increased over time. This may mean thyroid cancer cells are growing, and/or cancer is starting to spread.
- Little or no thyroglobulin was found. This may mean that your cancer treatment has worked to remove all thyroid cells from your body.
- Your thyroglobulin levels decreased for a few weeks after treatment, but then started to increase over time. This may mean your cancer has come back after you’ve been successfully treated.
If your results show that your thyroglobulin levels are increasing, your health care provider may prescribe additional radioiodine therapy to remove remaining cancer cells. Talk to your health care provider if you have questions about your results and/or treatment.
Is there anything else I need to know about a thyroglobulin test?
Although a thyroglobulin test is mostly used as a tumor marker test, it is occasionally used to help diagnose these thyroid disorders:
- Hyperthyroidism is a condition of having too much thyroid hormone in your blood.
- Hypothyroidism is a condition of not having enough thyroid hormone.
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