thyroglobulin
Reviewed
Also called: TGB, thyroglobulin tumor marker
A thyroglobulin test measures the amount of a protein called thyroglobulin (Tg) in a sample of your blood.
Specimen: blood
Why this test may be ordered
- Before starting treatment for thyroid cancer to establish a baseline
- 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 has not come back
- To monitor noncancerous thyroid conditions such as hyperthyroidism or hypothyroidism
Preparation and collection
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.
A health care professional will take a blood sample from a vein in your arm, using a small needle. This usually takes less than five minutes.
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.
Understanding results
Understanding the results of a thyroglobulin test after treatment can be complicated. The meaning of your results depends on your health history, the type of treatment you had, and the results of other tests.
- Very low levels or no thyroglobulin after treatment for thyroid cancer: Very low levels or no thyroglobulin may mean that your cancer treatment successfully removed all thyroid tissue, including cancerous tissue. Limitation: A thyroglobulin test may not be useful for monitoring your thyroid cancer treatment if you have thyroglobulin antibodies in your blood. Next step: However, you will still need more testing over time to make sure.
- Thyroglobulin levels that stay high or increase after treatment for thyroid cancer: Thyroglobulin levels that stay high or increase may mean that your treatment did not successfully remove all thyroid tissue or that you still have thyroid cancer. It may also mean that your cancer has grown and/or spread. Limitation: Because other thyroid conditions and certain illnesses can also affect thyroglobulin, your provider will likely check your levels over time instead of relying on a single test result. Next step: So, it’s best to ask your provider to explain what your test results say about your health.
- Thyroglobulin levels that were low after treatment but later increased: Thyroglobulin levels that were low after treatment but later increased may mean that your thyroid cancer has come back after treatment. Limitation: Because other thyroid conditions and certain illnesses can also affect thyroglobulin, your provider will likely check your levels over time instead of relying on a single test result. Next step: So, it’s best to ask your provider to explain what your test results say about your health.
- A thyroglobulin test alone cannot be used to diagnose cancer.
- Other thyroid conditions (hyperthyroidism, hypothyroidism, thyroiditis) and certain illnesses can affect thyroglobulin levels.
- Labs use different methods to measure thyroglobulin, which can affect results. It is important to have tests done the same way, usually in the same lab.
- Thyroglobulin antibodies in your blood can make thyroglobulin levels appear lower than they really are. Your provider will usually order a thyroid antibody test to find out whether thyroglobulin testing will be useful.
What to do next
So, it’s important to have your tests done the same way, and usually in the same lab. This allows your provider to compare your results over time.
- What do my thyroglobulin test results mean for my specific health situation?
- Do I need to have my tests done at the same lab each time?
- Should I be tested for thyroglobulin antibodies before relying on this test?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.