Thyroid antibodies are cells the immune system forms in response to thyroid cells. They develop when the immune system mistakenly attacks thyroid cells and tissues. High levels can indicate an autoimmune condition, such as Hashimoto’s disease.

Thyroid antibodies happen because the immune system mistakes thyroid cells for harmful cells and attacks them. However, the immune system might also create thyroid antibodies in response to cancer cells within the thyroid gland.

Therefore, doctors may test a person for elevated thyroid antibody levels to diagnose autoimmune diseases.

This article discusses thyroid antibody function and what conditions their presence might indicate. It also lists some common thyroid antibody tests and answers some common questions about thyroid antibodies.

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As a 2022 review explains, the thyroid is a gland within a person’s neck. It produces a variety of different thyroid hormones. These hormones help to regulate a person’s metabolism, as well as the process of protein formation.

As with any other organ, multiple cells compose the thyroid. Usually, other bodily systems do not interfere with those cells, allowing the thyroid gland to perform its function. However, it is possible for an individual’s immune system to attack and damage thyroid cells. This can cause various kinds of thyroid dysfunction.

The role of the immune system is to detect and destroy harmful pathogens, like bacteria, or viruses. However, in autoimmune conditions, a person’s immune system mistakes some of their own healthy cells for an invading pathogen.

Whenever the immune system reacts to a perceived threat, it releases biochemicals called antibodies. Thyroid antibodies develop when a person’s immune system attacks thyroid cells. These are healthy thyroid cells in autoimmune conditions.

There are several different kinds of thyroid antibodies. The British Thyroid Foundation (BTF) explains that different thyroid antibodies will cause different kinds of thyroid disorders. Therefore, the presence of thyroid antibodies can indicate the presence of several diseases.

Hashimoto’s thyroiditis

Hashimoto’s thyroiditis is an autoimmune condition that causes hypothyroidism (underactive thyroid gland). The condition is the most common cause of hypothyroidism in developed countries and it is more likely to arise in people with other autoimmune disorders.

Some common early symptoms of Hashimoto’s thyroiditis include:

The primary treatment for the condition is thyroid hormone replacement therapy.

Graves’ disease

Graves’ disease is a different autoimmune disease. It is the most common cause of hyperthyroidism (overactive thyroid gland). In the United States, around 1.2% of the population will develop Graves’ disease.

Some symptoms of the condition include:

Treatment for Graves’ disease may include:

There are several different kinds of thyroid antibody tests. The BTF lists some of them as follows:

  • Thyroid peroxidase antibody (TPOAb) test. People with Hashimoto’s thyroiditis have higher levels of TPOAb, and some people with Graves’ disease also have raised TPOAb levels.
  • Thyroglobulin antibody (Tg Ab) test. A doctor may monitor Tg Ab levels in people who have had thyroid cancer. Some people with Hashimoto’s thyroiditis also have elevated Tg Ab levels.
  • Thyroid-stimulating hormone receptor antibody (TSHR Ab/TRAb) test. People with Graves’ disease have higher levels of TSHR Ab.
  • Thyroid-stimulating immunoglobulin test. A person with Graves’ disease may have raised thyroid-stimulating immunoglobulin levels.

Doctors do not always use all these tests if they suspect that someone has a thyroid condition.

Below are some of the most common questions and answers about thyroid antibodies:

What causes thyroid antibodies to be high?

Thyroid antibody levels may increase when a person’s immune system mistakes healthy thyroid cells for harmful organisms, like bacteria or viruses.

Can thyroid antibodies go away?

In some cases.

For example, people with Graves’ disease may find their thyroid antibody levels go back to normal after treatment. However, thyroid antibodies can remain in the body for years after treatment and cause a relapse.

Generally, thyroid antibodies remain in the body in people with Hashimoto’s thyroiditis but the antibody levels can fluctuate.

What is a normal range for thyroid antibodies?

It depends on the type of thyroid antibody, alongside a variety of factors.

According to Thyroid UK, the reference range for Tg Ab should be less than 200 milli-international units per milliliter (mUI/ml) or an antibody index of no higher than 0.9. The reference range for TPOAb should be less than 150 mUI/ml or an antibody index of no higher than 0.9.

However, it is also important to note that different laboratories may have different reference ranges.

The immune system releases thyroid antibodies in response to thyroid cells. When thyroid cells are healthy, elevated thyroid antibodies can indicate an autoimmune condition, such as Graves’ disease or Hashimoto’s thyroiditis.

Therefore, a doctor may use a thyroid antibody test to diagnose autoimmune disorders. There are a number of different thyroid antibody tests a healthcare professional may use.