- Also Known As:
- Thyroglobulin Tumor Marker
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Test Quick Guide
Thyroglobulin (Tg) is a protein made by the thyroid gland. Tg can also be produced by certain types of thyroid cancer.
The thyroglobulin test is a type of tumor marker test used to measure the amount of Tg in the blood. Most often, doctors order Tg testing to evaluate the effectiveness of thyroid cancer treatment or to monitor for a recurrence of thyroid cancer after treatment is completed. Tg levels may also be measured to help diagnose certain non-cancerous conditions of the thyroid.
About the Test
Purpose of the test
The purpose of a Tg test is to measure the amount of thyroglobulin in the blood. Doctors routinely order thyroglobulin testing to manage patients with a history of papillary or follicular thyroid cancer, two of the most common types of thyroid cancer. Testing may be performed for several reasons, including:
- Postoperative evaluation: Tg testing can be used in patients recently treated for thyroid cancer to evaluate whether treatment was effective in eliminating thyroid cells in the body. Tg levels measured 6 to 12 weeks after successful surgical treatment should be very low.
- Monitoring for recurrence: A doctor may order thyroglobulin testing after a patient has completed treatment to check if cancer has returned, which is referred to as a recurrence. To monitor for a recurrence, doctors order periodic Tg testing alongside other tests like a physical exam and imaging tests.
- Prognosis: Thyroglobulin levels may be used to estimate survival rates and the likelihood that cancer will return, which is called a patient’s prognosis. For this purpose, doctors consider several Tg levels measured over time.
Some doctors may check thyroglobulin levels when diagnosing hyperthyroidism and hypothyroidism, thyroid disorders that are not cancer.
What does the test measure?
Thyroglobulin tests measure the amount of Tg in the blood.
Thyroglobulin is a protein produced by the thyroid gland. The thyroid gland is a small butterfly-shaped organ at the front of the neck and below the voice box. The thyroid produces the hormones triiodothyronine (T3) and thyroxine (T4), which play an important role in many body functions, including digestion, fertility, growth, and heart rate.
Before being released into the bloodstream, T3 and T4 are stored in the thyroid gland as thyroglobulin. In healthy people, the thyroid gland releases low levels of thyroglobulin into the bloodstream along with T3 and T4. However, papillary and follicular thyroid cancer also produce thyroglobulin. This means that people with thyroid cancer may have higher thyroglobulin levels than healthy individuals.
When should I get a thyroglobulin test?
Your doctor may recommend thyroglobulin testing if you are being treated for thyroid cancer. Recommendations for when you should get tested will depend on why your doctor is ordering a Tg test.
If you recently had surgery for thyroid cancer, your doctor may measure thyroglobulin levels to determine whether your treatment was successful in removing all of your thyroid cells, including both noncancerous and cancerous cells. This postoperative evaluation of Tg levels is usually ordered four to six weeks following surgery.
Testing is also performed periodically after treatment to monitor for thyroid cancer recurrence. Testing to measure Tg levels is usually ordered every three to six months during the first year following treatment. After initial treatment and follow-up, how often testing is needed varies based on unique features of the cancer and how the cancer responded to the initial treatment.
If your doctor is concerned about hyperthyroidism or hypothyroidism, they may order a thyroglobulin test to diagnose these conditions.
Finding a Thyroglobulin Test
How to get tested
A test to measure thyroglobulin levels must be ordered by a health professional. The sample needed to perform Tg testing is typically taken in a doctor’s office, medical clinic, or laboratory.
Can I take the test at home?
At this time, there are no at-home test kits available that measure thyroglobulin levels. Tg testing must be ordered by a doctor and your sample must be sent to a laboratory for analysis.
However, you can purchase at-home test kits that assess other substances related to thyroid function. More information about these test kits can be found on our page about at-home thyroid testing.
How much does the test cost?
The cost of a thyroglobulin test varies based on multiple factors including your insurance status, whether other tests are performed at the same time, and where testing is conducted.
When ordered by a doctor, testing is often covered by health insurance. It is important to talk with your doctor, laboratory, or health insurance company about out-of-pocket costs you may be responsible for including copays and deductibles.
Taking the Thyroglobulin Test
Thyroglobulin testing is performed on a sample of blood. The blood sample is often collected from your arm in a doctor’s office, medical clinic, or laboratory.
Before the test
Typically, no special test preparation is needed before a Tg test. If you have questions about how to prepare for testing, you can speak with your doctor. It is important to follow any pre-test instructions provided by your doctor or the laboratory to ensure an accurate result.
During the test
Thyroglobulin tests require a sample of blood drawn from a vein, often collected from the inside of your elbow. The health professional drawing your blood will typically place an elastic band called a tourniquet around your upper arm to increase the amount of blood in your vein. A needle is then inserted into the vein to begin the collection process. Blood will flow through the needle into a test tube or small vial.
The procedure to draw your blood usually takes a few minutes. You might feel a slight pain or stinging sensation in your arm where the needle is inserted, but the discomfort should not last long.
After the test
Once the health professional removes the needle from your vein, they apply pressure and a bandage to the area. This will stop the flow of blood and help to prevent bruising.
Usually, you can return to your normal activities following your blood draw. If you notice continued bleeding, discomfort, or signs of infection at the procedure site, you should speak with your doctor.
Thyroglobulin Test Results
Receiving test results
Your doctor should have the results of your Tg test within several business days. They may contact you to provide results over the phone or to schedule an appointment to talk more about your test result and next steps in your care.
If you have access to an electronic medical record, your doctor may upload the results of your test online. You may also receive a copy of your result in the mail.
Interpreting test results
Your test report will provide information about the level of thyroglobulin detected in the blood in nanograms per milliliter (ng/mL). Your report will also include a reference range used to interpret your result. A reference range is the expected range that helps doctors determine what is considered for a healthy population.
Different methods can be used to perform thyroglobulin testing on a blood sample. The test methods used may vary from laboratory to laboratory. Other factors, such as the type of initial treatment and the presence of anti-thyroglobulin antibodies, can also affect your test results.
After successful treatment for thyroid cancer, Tg levels should drop significantly. Elevated levels following treatment can suggest that treatment was unsuccessful in removing all thyroid tissue from the body, that thyroid cancer has spread to other areas of the body, or that you may be experiencing a recurrence of cancer.
Because your doctor is the most familiar with your medical history and current health status, they are in the best position to interpret your test result and say what these results mean for your health.
Are test results accurate?
Tests that measure thyroglobulin levels are widely used and are generally considered accurate. However, no test is perfect and several factors can influence the reliability of your test result.
Thyroglobulin antibodies, also known as antithyroglobulin (anti-Tg) antibodies, are proteins produced by the immune system that attack healthy thyroid tissue. Thyroglobulin antibodies
bind to Tg. Because Tg testing can’t detect Tg that is bound to thyroglobulin antibodies, anti-Tg antibodies can cause your test result to appear low. Doctors typically order Tg and anti-Tg antibody tests at the same time to account for this and improve the reliability of testing.
Multiple methods are available to perform thyroglobulin testing on a blood sample. The same testing method should be used each time the test is performed, as there is variability among test methods. Results from Tg tests taken over time using different methods cannot be directly compared.
Some studies suggest that the dietary supplement biotin may influence thyroglobulin levels, although more research is needed to confirm this finding. If you take biotin supplements, you may wish to talk to your doctor about any possible impact on your Tg test results. You can also ask your doctor whether they recommend having another Tg test after not taking biotin.
You can talk with your doctor about the reliability and significance of your Tg test result given your situation.
Do I need follow-up tests?
If you have an elevated thyroglobulin level after treatment for thyroid cancer, additional testing may be suggested depending on your situation. Your doctor may suggest a physical exam, imaging tests, or a biopsy to learn more.
If you need follow-up testing, your doctor can provide information about the tests that are recommended for your situation and the risks and benefits of each test.
Questions for your doctor about test results
It is normal to have questions about the results of laboratory tests. Your doctor can help answer questions about your results and what they mean in the context of your overall health. Here are some questions you may want to ask your doctor about thyroglobulin testing:
- What were my thyroglobulin test results?
- What does the result of my test tell you about the status of my thyroid cancer?
- How often will I have testing to measure my thyroglobulin level?
- Do you recommend other testing based on the results of my Tg test?
- Do I have anti-thyroglobulin antibodies?
Thyroglobulin test vs. thyroglobulin antibody test
Thyroglobulin tests measure the Tg protein in the bloodstream. Thyroglobulin antibody tests detect Tg antibodies that are produced by the immune system and can cause damage to the thyroid.
Thyroid antibodies can influence the accuracy of Tg test results, making it more difficult to find a cancer recurrence. Doctors order both Tg and TgAb tests when measuring thyroglobulin levels to check for thyroid cancer recurrence.
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