What is Anti Thyroglobulin Antibody / Anti Tg/Tg Ab?
Also Known As:
Thyroid Peroxidase, TPO, Microsomal Antigen, Anti-TPO Antibodies, Thyrotropin Receptor Antibodies, TRAbs, Stimulating Antibodies, Thyroid-Stimulating Antibodies, Thyroid-Stimulating Immunoglobulins, TSI, Thyroid-Stimulating Hormone Receptor Antibody, TSH Receptor Antibodies, TSH Receptor-Binding Inhibitor Immunoglobulin, TBII, TBI, Thyroglobulin Antibody, TgAb, Thyroid Autoantibodies
Thyroid Peroxidase Antibody Thyroglobulin Antibody Thyroid Stimulating Hormone Receptor Antibody
Thyroid antibodies develop when a person’s immune system mistakenly targets components of the thyroid gland or thyroid proteins. This autoimmune response, in which the immune system mistakenly damages tissues in the body, can lead to chronic inflammation of the thyroid, tissue damage, and/or disruption of thyroid function.
Laboratory tests detect the presence and measure the number of specific thyroid antibodies in the blood. Understanding the underlying cause of thyroid dysfunction can help doctors plan the best course of treatment for patients.
Purpose of the test
Thyroid antibody tests are used for several purposes. Often, they are used to determine what is causing hypothyroidism or hyperthyroidism. Hypothyroidism describes an underactive thyroid gland, while hyperthyroidism describes an overactive thyroid gland. Thyroid antibody tests may also be used for the following purposes:
- To diagnose an autoimmune disorder, such as Hashimoto’s thyroiditis or Graves’ disease
- To define the best course of treatment
- To determine whether patients with mild hypothyroidism are likely to get worse over time
- To evaluate the risk to the fetus in pregnant individuals with thyroid disease
- To estimate the risk of relapse after treatment for Graves’ disease
- To monitor patients previously treated for thyroid cancer
In the U.S., most cases of hypothyroidism and hyperthyroidism are caused by autoimmune diseases, such as Graves’ disease and Hashimoto’s thyroiditis, in which the immune system interferes with the normal functioning of the thyroid gland. Hashimoto’s thyroiditis is so common in the U.S. that it is often assumed to be the cause of an underactive thyroid. While Graves’ disease is present in 70% of patients diagnosed with hyperthyroidism.
Although detecting thyroid antibodies can support a diagnosis of Graves’ disease or Hashimoto’s thyroiditis, it is not always necessary to test thyroid antibodies in order to diagnose an autoimmune disorder affecting the thyroid gland.
What does the test measure?
Thyroid antibody testing detects and measures thyroid antibodies in the blood. Normally, antibodies attack foreign substances in the body, like bacteria, viruses, parasites, and toxins.
In patients with autoimmune disorders, antibodies mistakenly target the body’s own tissues. These antibodies that attack the patient’s own body are also known as autoantibodies or antithyroid antibodies. Thyroid antibody testing may look for several types of thyroid antibodies:
- Thyroid peroxidase antibodies (TPOAb): Thyroid peroxidase is an enzyme that is crucial to the production of thyroid hormones. TPOAb may interfere with the action of this enzyme. Almost all patients with Hashimoto’s thyroiditis have high levels of TPOAb.
- Thyroglobulin antibodies (TgAb): Thyroglobulin is a protein made by the thyroid gland. TgAb may be present when the thyroid has been damaged. Thyroglobulin antibodies are often measured in addition to thyroglobulin tests after a patient completes treatment for thyroid cancer.
- Thyrotropin receptor antibodies (TRAb): TRAb are antibodies that bind to the receptors on thyroid cells normally activated by thyroid-stimulating hormone (TSH). In Graves’ disease, an antibody called thyroid-stimulating immunoglobulin (TSI) binds to the TSH receptor and mimics the action of TSH. This causes constant stimulation of the thyroid gland, prompting it to release too much thyroid hormone into the bloodstream. Stimulation by TSI can also cause abnormal growth of the thyroid gland.
When should I get testing for thyroid antibodies?
It is not always necessary to test for thyroid antibodies to establish a diagnosis of an autoimmune disorder affecting the thyroid. However, doctors may find thyroid antibody testing helpful in the following situations:
- Subclinical hypothyroidism: In patients with a high TSH and a normal T4, testing for TPO antibodies may help predict whether the hypothyroidism will progress from being subclinical, in which it may not be causing significant or observable symptoms, to more severe and permanent dysfunction.
- Goiter: A goiter describes the abnormal enlargement of the thyroid gland. Some experts recommend testing for TPOAb in patients with a goiter, even if their thyroid hormone levels are normal.
- Hyperthyroidism, if the cause is not obvious: When patients have an overactive thyroid, sometimes it is clear from their physical examination and thyroid hormone tests that they have Graves’ disease. In less obvious cases, TRAb testing or imaging tests may be helpful in diagnosing or ruling out Graves’ disease.
- Monitoring after thyroid cancer treatment: Patients who are monitored with thyroglobulin testing after treatment may also have their TgAb levels tested as elevated TgAb can interfere with some thyroglobulin tests.
Although thyroglobulin antibodies may be elevated in both Hashimoto’s and Graves’ disease, it is not typically tested during diagnosis.
How to get tested
Thyroid antibody tests are typically ordered by a doctor after other blood tests suggest a potential thyroid disorder. A blood sample is used for testing and can be taken at a doctor’s office, clinic, lab, hospital, or other medical settings.
Can I take the test at home?
Test kits are available that allow patients to test for certain thyroid antibodies at home. These kits provide the supplies needed for obtaining a blood sample and returning it to the company for analysis.
Some kits include one or more thyroid antibody tests as part of a panel of thyroid tests, while others test only for TPOAb or TgAb. At-home tests for TRAb may not be commercially available at this time.
Thyroid antibody tests are difficult to interpret and may be unnecessary if other thyroid tests are normal. If an abnormal level of thyroid antibodies is detected on an at-home test, it is likely that an endocrinologist will want the test to be repeated.
In-depth information about at-home thyroid testing is available at the At-Home Thyroid Testing page.