Thyroglobulin antibody (TgAb) is a special autoantibody that targets thyroglobulin protein in the thyroid, but how TgAb affects the thyroid remains unknown.
TgAb tests are useful when checking for recurrence of thyroid cancer after removal of the thyroid gland through a thyroidectomy.
TgAb is also implicated in autoimmune thyroid diseases such as Graves’ disease and Hashimoto’s disease.
Our bodies are great at protecting us from viruses, toxins, and many foreign substances. The immune system produces proteins called antibodies that act as the body’s first line of defense against infections. Sometimes, though, our bodies will produce antibodies that mistakenly target our own cells. These antibodies are called autoantibodies.
Autoantibodies can exist all over the body or be concentrated in one specific tissue. For example, the thyroglobulin antibody is a type of autoantibody produced in the thyroid that affects the thyroid protein thyroglobulin. Autoantibodies like the thyroglobulin antibody are studied in great detail because they are linked to autoimmune diseases. In fact, in 1956, the thyroglobulin antibody became the first antibody identified in an individual with autoimmune thyroid disease.
The thyroglobulin antibody, also known as the antithyroglobulin antibody, is often abbreviated TgAb. TgAb attacks thyroglobulin, a special protein in the thyroid gland. Thyroglobulin helps build thyroid hormones by storing iodine. When TgAb attacks thyroglobulin, thyroid function may be compromised.
So does TgAb alone affect your thyroid? There is evidence that TgAb can interact with thyroid cells, but researchers do not yet know if thyroglobulin antibodies themselves cause damage to the thyroid tissue. (Source)
Autoantibodies can be harmful if they destroy healthy tissue, but autoantibodies also play an important role in autoantibody tests. A TgAb test, for example, is used to:
We go into detail on each of these uses below.
A TgAb test is performed like a general serum, or blood, test. Once your blood is drawn, a special test called an immunoenzymatic assay is performed to measure the serum thyroglobulin antibody level. Generally, each laboratory that performs this test has their own scale for TgAb levels and will report your results as either negative or positive. (Source)
A negative result means there is little to no thyroglobulin autoantibody present in your sample and you likely do not have a thyroid disorder.
A positive result, on the other hand, means there is thyroglobulin autoantibody present in your sample and you may have a thyroid disorder. (Source)
One of the reasons TgAb tests are useful is because they can clue in health care providers to a thyroid disorder that their patient may have. There are a few thyroid disorders that cause elevated TgAb levels.
We say that TgAb is highly specific for Hashimoto’s disease and Graves’ disease because TgAb is found in the majority of patients who are diagnosed with these autoimmune thyroid diseases. TgAb is present in 60%–80% of patients who have Hashimoto’s disease and 50%–60% of patients with Graves’ disease.
Like other antibody tests, the TgAb test is commonly performed along with a test for a different antibody. For example, a TPOAb (thyroid peroxidase antibody) test is generally performed in addition to the TgAb test to test for Hashimoto’s disease.
To diagnose Graves’ disease, a TRAb (thyrotropin receptor antibody) test is often used in addition to the TgAb test because the TgAb test is not as accurate in diagnosing Graves’ disease. (Source, Source)
In general, a TgAb test is used to confirm a diagnosis of Hashimoto’s disease after an individual presents with the common symptoms of the disease. Hashimoto’s disease, or Hashimoto’s thyroiditis, is an autoimmune thyroid disease that is associated with high levels of TgAb. Hashimoto’s disease is also the main cause of hypothyroidism, or an underactive thyroid gland. Hypothyroidism results when the thyroid is not producing sufficient thyroid hormones because the thyroid is under attack by autoantibodies, such as TgAb. (Source)
However, around 10%–15% of individuals who are diagnosed with Hashimoto’s disease have a negative antibody test result. This means that while a positive antibody test is a strong indicator of an autoimmune disease, there is no causal relationship. You can receive a negative TgAb test result and be diagnosed with Hashimoto’s disease, or you can receive a positive TgAb test result and not be diagnosed with Hashimoto’s disease.
Some common symptoms of Hashimoto’s disease are:
Although an elevated TgAb level can be a marker of Hashimoto’s disease, individuals with Graves’ disease can also have elevated TgAb levels. Graves’ disease is an autoimmune disease that is characterized by an overactive and enlarged thyroid gland.
Overactivity of the thyroid is called hyperthyroidism. Hyperthyroidism in Graves’ disease is caused by thyroid autoantibodies that target receptors for thyroid-stimulating hormone (TSH), which is released by the pituitary gland to stimulate production of thyroid hormones. These receptor antibodies are the main antibodies that are present at elevated levels in Graves’ disease.
If you are experiencing symptoms of Graves’ disease and receive a positive thyroid antibody test, such as a TgAb test, these are two indicators that you have Graves’ disease.
Some common symptoms of Graves’ disease are:
Although there are common symptoms for Hashimoto’s disease and Graves’ disease, researchers do not know if elevated TgAb levels alone cause symptoms. This stems from the fact that we do not know if TgAb damages the thyroid and we do not know the mechanism through which TgAb affects the thyroid. (Source)
Thyroid disorders can affect your pregnancy. If you are pregnant and have Hashimoto’s disease or Graves’ disease, you will need to have your hormone levels measured throughout your pregnancy. There is evidence that having elevated levels of thyroid antibodies such as TgAb can interfere with how your thyroid gland responds to a pregnancy hormone called human chorionic gonadotropin (hCG). This hormone is important for maintaining pregnancy, and if the thyroid cannot properly respond to this hormone, there is risk of loss of the pregnancy. (Source, Source)
Some studies have associated thyroid antibodies with adverse pregnancy outcomes such as miscarriage or preterm delivery. However, these studies focus on antibodies against TSH rather than against thyroglobulin. There is no current evidence thatWe don’t know if elevated levels of TgAb would affect pregnant women in the same way. (Source, Source)
Overall, there are mixed findings and researchers cannot conclude there is a causal relationship between elevated levels of TgAb and adverse pregnancy outcomes.
If you are diagnosed with thyroid cancer, one treatment option isyou may choose to have your thyroid removed in a procedure known as a thyroidectomy. After a thyroidectomy, no thyroid tissue is expected to be presentwe expect there to be no thyroid tissue present.
Thyroglobulin is produced by both normal thyroid cells and cancerous thyroid cells, and after a thyroidectomy, Tg levels are expected to be very low we expect very low Tg levels. Monitoring levels of both Tg and TgAb in your blood helps make sure there is no remaining thyroid tissue or cancer cells.
Why does the level of TgAb matter? After a thyroidectomy, the presence of TgAb can cause inaccurate measurement of Tg levels. Measuring both Tg and TgAb ensures an accurate representation of thyroid tissue present.
Also, TgAb levels are elevated in individuals with differentiated thyroid cancer. While individuals without thyroid cancer have TgAb levels of about 10%, individuals with thyroid cancer have TgAb levels around 25%. This statistic tells us that TgAb is a strong indicator of cancer recurrence after a thyroidectomy.
Although TgAb tests come in handy after a thyroidectomy, we don’t have sufficient evidence to conclude that TgAb levels can be used to predict likelihood of developing or having a recurrence of thyroid cancer.
A positive TgAb test is one indicator that you may have a thyroid disorder such as Hashimoto’s disease or Graves’ disease. Your symptoms and the results of other thyroid tests will help reach a diagnosis. Both of these autoimmune thyroid diseases can be managed through science-backed remedies and prescribed medication.