Antibodies that Contribute to Thyroid Disease
October 1, 2019
While there are a number of different thyroid disorders, autoimmune antibodies against the thyroid gland are among the most well-understood causes of thyroid disease. Because of this, your doctor may order thyroid antibody tests for you. These results can help identify the root cause of your thyroid disease and may factor into a treatment plan for your condition.
Antibodies are proteins produced by your body to help protect you against infections. They can, however, mistakenly attack your own tissues, causing illness. The consequence is described as an autoimmune disease, and some thyroid conditions are caused by this immune system dysfunction.
There are several types of thyroid antibodies, and each one attacks a different target in the thyroid hormone production process, ultimately causing thyroid disease.
The most common thyroid antibodies are:1
Anti-thyroperoxidase (TPO) Antibodies
The most common thyroid antibodies attack thyroid peroxidase.Also called thyroperoxidase (TPO), this enzyme functions in the thyroid gland to help produce the thyroid hormones thyroxine (T4) and triiodothyronine (T3).
Autoimmune antibodies can interfere with TPO's ability to use iodine to produce these hormones, resulting in hypothyroidism. TPO antibodies cause inflammation, can eventually destroy all or part of your thyroid gland, and can also cause your thyroid gland to form nodules or to become enlarged.
The presence of anti-TPO antibodies is associated with pre-term labor and with Hashimoto's thyroiditis, an autoimmune thyroid condition.
Thyroid Stimulating Hormone (TSH) Receptor (TSHR-Ab) Antibodies
Anti-thyroglobulin (Anti-Tg) Antibodies
Thyroglobulin (Tg) is a protein that helps the thyroid gland function properly. Anti-Tg antibodies are associated with thyroid cancer. Some people who have thyroid cancer have both anti-Tg and anti-TPO antibodies.
Antibody levels can be determined by analyzing a blood sample. Normal values are as follows:
- TPO antibody: The measured serum level should be less than 9 IU/mL.
- Anti-Tg antibody: The measured serum level should be less than 4 IU/mL.
- Thyroid-stimulating immunoglobulin antibody (TSI): This value should be less than 1.75 IU/L.
*Note, however, that normal range values may differ based on the laboratory where you are getting your test.
What Anti-Thyroid Antibodies Mean for You
Generally speaking, your thyroid treatment is not based on antibody levels—it is based on your symptoms and thyroid hormone levels. However, antibody tests can be useful in assessing the cause of your thyroid disease and can help identify subclinical thyroid disease.
Positive thyroid antibodies suggest that you could have autoimmune thyroid disease, but they are only a piece of the picture.1 While they may influence the decision to move ahead with treatment, other factors in addition to your symptoms—family history, other blood test results—will be considered, too.
If you have high levels of thyroid antibodies without symptoms and with normal thyroid hormone levels, your doctor is less likely to treat your thyroid disease than if you have mild symptoms or borderline abnormal thyroid hormone levels along with your elevated antibody levels.
Sometimes, the presence of antibodies supports the diagnosis of subclinical hypothyroidism, which is thyroid disease with minimal symptoms or without symptoms. Early therapy for subclinical thyroid disease may prevent its progression, but this has not been validated.
A Word From Verywell
Usually, autoimmune disease affects one or a few organs in the body. But if you have one autoimmune disease, it increases your chances of having another as well. Autoimmune thyroid disease is often associated with other conditions that are believed to have an autoimmune etiology, like diabetes and inflammatory bowel disease.