Antibodies That Contribute to Thyroid Disease

Thyroid disorders can have many causes. Autoimmune disorders of the thyroid are the most well-understood.

If you have symptoms of a thyroid disorder, your healthcare provider may order antibody tests. These tests can help identify the cause of your disease. They may also help your healthcare provider decide on a treatment plan.

This article discusses anti-thyroid antibodies, what they do, and why you may need an antibody test. It will also help you understand what your test results mean.

Autoimmune Antibodies and Thyroid Disease

The thyroid is a gland located in the front of your neck. It produces important hormones that help control your metabolism and other body functions. 

Your thyroid gets its instructions from the pituitary gland, a small structure in your brain. The pituitary gland releases thyroid stimulating hormone (TSH), which tells the thyroid gland to make thyroid hormone.

Antibodies are proteins your immune system makes to help protect you against infections. Sometimes antibodies can mistakenly attack your own tissues.

Some thyroid conditions happen because antibodies attack the gland and interfere with its normal hormone-making process. These conditions are called autoimmune diseases of the thyroid.

The most common thyroid antibodies are:

• Anti-thyroperoxidase (TPO) antibodies
• Thyroid stimulating hormone (TSH) receptor antibodies (TSHR-Ab)
  
• Anti-thyroglobulin (anti-Tg) antibodies

Anti-thyroperoxidase (TPO) antibodies

The most common thyroid antibodies attack thyroid peroxidase (TPO). TPO is an enzyme in the thyroid gland that helps produce two important thyroid hormones:

• Thyroxine (T4)
• Triiodothyronine (T3)

TPO uses iodine, an important nutrient, to produce these hormones. Autoimmune antibodies stop TPO from using iodine. This causes hypothyroidism, which is when your thyroid doesn't make enough hormones.

Anti-TPO antibodies cause inflammation that can eventually destroy all or part of your thyroid gland. The inflammation can also cause it to form nodules or to become enlarged.

Anti-TPO antibodies are associated with an autoimmune condition called Hashimoto's disease. People with Hashimoto's disease may have low thyroid hormone levels, but high TSH levels. This is because the pituitary gland produces more TSH to try to tell the thyroid to make more hormone.

In pregnant people, TPO antibodies are also associated with preterm labor and other problems.

It may take time for TPO antibodies to cause a measurable change in your TSH levels. You can have positive TPO antibodies for months or years before you are diagnosed with hypothyroidism. Some people with positive TPO antibodies never become hypothyroid.

Thyroid Stimulating Hormone (TSH) Receptor Antibodies (TSHR-Ab)

TSH starts the hormone-making process by binding to structures on the thyroid gland called TSH receptors. TSH receptor antibodies (TSHR-Ab) can imitate the action of TSH. This causes hyperthyroidism, when the thyroid makes too much hormone.

TSHR antibodies are also called thyroid-stimulating immunoglobulins (TSI). High levels are associated with an autoimmune condition called Graves' disease.

Anti-thyroglobulin (Anti-Tg) Antibodies

Thyroglobulin (Tg) is a protein that helps the thyroid gland function properly. Anti-Tg antibodies attack thyroglobulin. This can cause hypothyroidism.

Anti-Tg antibodies are also associated with Hashimoto's disease.

Thyroid Antibody Test Results

Antibody levels can be tested with a blood sample. The antibody test measures the amount of antibody per milliliter or liter of blood in "international units."

Normal values are:

• TPO antibody: Less than 9 IU/mL
  
• Thyroid-stimulating immunoglobulin antibody (TSI): Less than 1.75 IU/L
• Anti-Tg antibody: Less than 4 IU/mL

Note that different laboratories may have different normal range values.

What Anti-Thyroid Antibodies Mean for You

Thyroid treatment is not based on antibody levels. Treatment is based on symptoms and thyroid hormone levels.

Antibody tests are useful in finding the cause of your thyroid disease. They can also help identify subclinical thyroid disease, which is thyroid disease with mild or no symptoms.

Positive thyroid antibodies suggest you could have autoimmune thyroid disease. Still, they are only a piece of the picture. They can help healthcare providers decide if treatment is needed. Healthcare providers will also consider your symptoms, family history, and other blood test results.

The presence of antibodies may confirm subclinical hypothyroidism. Early therapy might prevent disease progression, but this has not been proven.

Summary

Some thyroid conditions are caused by autoimmune disorders. These are conditions where the body produces antibodies that interfere with the thyroid hormone-making process.

Thyroid antibodies may cause the thyroid to make too much or not enough thyroid hormone. An antibody test can determine the cause of your condition.

Thyroid treatment is based on your symptoms. If you do not have symptoms, you may not need treatment.

A Word From Verywell

Autoimmune diseases usually only affect one or a few organs. Still, if you have one autoimmune disease, you have a greater chance of having another one.

Autoimmune thyroid disease can be associated with other conditions thought to have autoimmune causes. This includes diabetes and inflammatory bowel disease.