Thyroid disease can have many causes. The most studied autoimmune diseases of the thyroid gland.
If you have symptoms of thyroid disease , your healthcare provider may order antibody tests. These tests can help determine the cause of your condition. They can also help your healthcare provider decide on a treatment plan.
This article looks at thyroid antibodies, how they work, 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 gland is a gland located in the front of the neck. It produces important hormones that help control metabolism and other bodily functions.
Your thyroid gland receives instructions from the pituitary gland , a small structure in your brain. The pituitary gland produces a thyroid-stimulating hormone (TSH), which tells the thyroid gland to make thyroid hormone.
Antibodies are proteins that your immune system makes to protect you from infection. Sometimes antibodies can mistakenly attack your own tissues.
Some thyroid disorders occur when antibodies attack the gland and interfere with normal hormone production. These conditions are called autoimmune thyroid diseases.
There are several types of thyroid antibodies. Each of them attacks a different target in the production of thyroid hormones.
The most common thyroid antibodies are:
- Thyroid peroxidase (TPO) antibodies
- Thyroid-stimulating hormone (TSH) receptor (TSHR-Ab) antibodies
- Thyroglobulin antibodies (anti-TG)
Thyroid peroxidase (TPO) antibodies
The most common thyroid antibodies attack thyroid peroxidase ( TPO ). TPO is a thyroid enzyme that helps in the production of two important thyroid hormones:
- Thyroxine (T4)
- Triiodothyronine (T3)
TPO uses iodine, an essential nutrient, to produce these hormones. Autoimmune antibodies prevent TPO from using iodine. It causes hypothyroidism when the thyroid gland does not produce enough hormones.
Antibodies to TPO cause inflammation, which can eventually destroy all or part of the thyroid gland. The inflammation can also cause nodules or enlargement.
Antibodies against TPO have been linked to an autoimmune disease 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 force the thyroid to produce more hormones.
In pregnant women, TPO antibodies are also associated with preterm labor and other problems.
It can take time for TPO antibodies to cause a measurable change in TSH levels. You may have positive antibodies to TPO for months or years before being diagnosed with hypothyroidism. Some people with positive antibodies to TPO never develop hypothyroidism.
Thyroid-stimulating hormone (TSH) receptor (TSHR-Ab) antibodies
TSH triggers the production of hormones by binding to structures in the thyroid gland called TSH receptors. Antibodies against TSH receptors (TSHR-Ab) can mimic the action of TSH. It causes hyperthyroidism when the thyroid gland produces too many hormones.
TSHR antibodies are also called thyroid-stimulating immunoglobulins (TSI). High levels are associated with an autoimmune disorder called Graves' disease .
Thyroglobulin Antibodies (Anti-Tg)
Thyroglobulin (TG) is a protein that helps the thyroid gland work properly. Antibodies against TG attack thyroglobulin. This can lead to hypothyroidism.
Antibodies against Tg are also associated with Hashimoto's disease.
Thyroid antibodies attack various parts of the hormone production process. This can cause the thyroid gland to make too much or too little hormones.
Thyroid antibody test results
Antibody levels can be checked with a blood sample. The antibody test measures the amount of antibodies per milliliter or liter of blood in "international units."
- Antibodies against TPO: less than 9 IU / ml.
- Thyroid-stimulating immunoglobulin antibodies (TSI): less than 1.75 IU / L.
- Antibodies against Tg: less than 4 IU / ml.
Note that different labs may have different normal range values.
What do thyroid antibodies mean to you?
Treatment of the thyroid is independent of antibody levels. Treatment is based on your symptoms and thyroid hormone levels.
Antibody tests are helpful in determining the cause of your thyroid disorder. They can also help identify a subclinical thyroid disease , that is, a thyroid disease with little or no symptoms.
Positive thyroid antibodies suggest that you may have an autoimmune thyroid disorder. However, this is only part of the picture. They can help healthcare providers decide if treatment is needed. The healthcare provider will also consider your symptoms, family history, and other blood test results.
You may have elevated thyroid antibodies and do not need treatment. For example, if you are asymptomatic and your thyroid hormone levels are normal, your doctor may not be treating you. If you have mild symptoms or borderline thyroid levels, you are more likely to receive treatment.
The presence of antibodies can confirm subclinical hypothyroidism. Early therapy can prevent disease progression, but this has not been proven.
Some thyroid disorders are caused by autoimmune diseases. These are conditions in which the body produces antibodies that interfere with the production of thyroid hormones.
Thyroid antibodies can cause the thyroid gland to make too much or too little thyroid hormones. An antibody test can determine the cause of your condition.
Treatment of the thyroid gland depends on your symptoms. If you are asymptomatic, you may not need treatment.
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Autoimmune diseases generally affect only one or a few organs. However, if you have an autoimmune disease, you are more likely to develop another.