Test Quick Guide

Thyroglobulin (Tg) is a protein made by the thyroid gland. Certain types of thyroid cancer can also produce Tg.

The Tg 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 recurrence 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 the protein in the blood. Doctors routinely order Tg 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 Testing can be used if you have recently been treated for thyroid cancer to evaluate whether treatment effectively eliminated thyroid cells in the body. Tg levels measured six to 12 weeks after successful surgical treatment should be very low.
  • Monitoring for recurrence A doctor may order Tg testing after you have completed treatment to check if the cancer has returned, which is referred to as a recurrence. Doctors order periodic Tg testing alongside other tests like a physical exam and imaging tests to monitor for recurrence.
  • Prognosis Tg levels may be used to estimate survival rates and the likelihood that cancer will return, which is called your prognosis. For this purpose, doctors consider several Tg levels measured over time.

Some doctors may check Tg levels when diagnosing hyperthyroidism and hypothyroidism, thyroid disorders that are not cancer.

What does the test measure?

Tg tests measure the amount of Tg in the blood.

The thyroid gland, a small butterfly-shaped organ at the front of the neck and below the voice box, produces the protein. This gland 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 Tg into the bloodstream along with T3 and T4. However, papillary and follicular thyroid cancer also produce Tg. If you have thyroid cancer, you may have higher Tg levels than healthy individuals.

When should I get this test?

Your doctor may recommend Tg testing if you are being treated for thyroid cancer. Recommendations for when you should get tested depend on why your doctor is ordering a Tg test.

If you recently had surgery for thyroid cancer, your doctor may measure Tg levels to determine whether your treatment successfully removed all of your thyroid cells, including 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. Tests to measure Tg levels are 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 the unique features of the cancer and how it responds to the initial treatment.

If your doctor is concerned about hyperthyroidism or hypothyroidism, they may order a Tg test to diagnose these conditions.

Finding a Thyroglobulin Test

How can I get a thyroglobulin test?

A health professional must order a test to measure Tg levels. 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?

Currently, no at-home test kits are available that measure Tg levels. A doctor must order testing, 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 Tg 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 a Thyroglobulin Test

Tg 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

Tg 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, 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 schedule an appointment to discuss your test result and the next steps in your care.

If you have access to an electronic medical record, your doctor may upload your test results 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 Tg 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 an expected range that helps doctors determine what is considered a healthy population.

Different methods can be used to perform Tg 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-Tg 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, 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.

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 Tg testing:

  • What were my Tg 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 Tg level?
  • Do you recommend other testing based on the results of my Tg test?
  • Do I have anti-Tg antibodies?

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