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 may 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. Thyroglobulin antibody (TgAb), which targets the thyroglobulin protein produced by the thyroid gland, is one of the three most common thyroid autoantibodies. In this article we’ll look at what thyroglobulin and the thyroglobulin antibody are, and what it means if you test positive for the thyroglobulin antibody. (Source, Source)
What Is Thyroglobulin?
Thyroglobulin is a protein produced in the thyroid gland. It stores iodine and other components needed to produce the thyroid hormones tetraiodothyronine (T4) and triiodothyronine (T3). When T4 and T3 are needed, thyroglobulin is broken down and the hormones are released to circulate to other parts of the body. (Source)
What Is the Thyroglobulin Antibody?
The thyroglobulin antibody targets thyroglobulin. When TgAb attacks thyroglobulin, your body’s ability to make essential thyroid hormones like T4 and T3 is compromised.
Thyroglobulin antibody, along with anti-thyroid peroxidase (TPO) and anti-thyroid-stimulating hormone receptor (TSHR) antibodies, is often detected in people who have autoimmune thyroid diseases. Healthy people without autoimmune thyroid diseases may also have very low levels of TgAb that don’t trigger an autoimmune response. (Source)
Thyroglobulin Antibody Test
A TgAb test is used to:
- help diagnose autoimmune thyroid diseases such as Hashimoto’s thyroiditis and Graves’ disease. If you are experiencing symptoms of an autoimmune thyroid disease, a health care provider may order a TgAb test to check for thyroid problems.
- help diagnose certain kinds of thyroid cancer
- detect recurrence of thyroid cancer after the thyroid gland has been removed
Thyroglobulin Antibody Test on Blood
A TgAb test is performed as 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)
How Do I Interpret My TgAb Test Results?
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)
Elevated TgAb Levels and Thyroid Disorders
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 look 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)
TgAb and Hashimoto’s Disease
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:
- low levels of thyroid hormones
- slowed speech
- weight gain
- high blood pressure
- facial swelling
- abnormal tongue size
- slowed heart rate
TgAb and Graves’ Disease
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:
- high levels of thyroid hormones
- weight loss
- muscle weakness
- elevated heart rate
- goiter, or enlargement of the thyroid gland
- inflammation of the eyes
- irregular menstrual cycle
Symptoms of Elevated TgAb Levels
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)
What if I’m Pregnant?
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. Only one preliminary study, carried out on mice, found a higher rate of early pregnancy loss in the presence of TgAb. (Source, 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.
What if I’ve Had Thyroid Cancer?
If you have had thyroid cancer, thyroglobulin and TgAb levels were likely part of your initial diagnosis, and were probably followed after your treatment. If you had surgery that removed part or all of your thyroid gland, thyroglobulin and TgAb levels would have been expected to drop off after the surgery. Steady levels, and especially rising levels, after cancer treatment suggests cancerous tissue is still present and further treatment is needed. If you have had thyroid cancer, your care provider will help interpret your TgAb levels. (Source, Source)
The Bottom Line on the Thyroglobulin Antibody Test
A positive TgAb test is one indicator that you may have a thyroid disorder such as Hashimoto’s disease or Graves’ disease, although the role TbAb plays in these conditions is uncertain. Your symptoms and the results of other thyroid tests will help reach a diagnosis. Thyroglobulin antibody levels are also monitored after treatment for thyroid cancer.