What is a thyroid antibody test?

A thyroid antibody test measures the level of thyroid antibodies in a sample of your blood. Your thyroid is a small, butterfly-shaped gland in your neck. It makes hormones that control many activities in your body, including your heart rate and how fast you burn calories from food.

Antibodies are proteins that your immune system makes to fight foreign substances, such as viruses and bacteria. But sometimes antibodies attack the healthy cells of your own tissues and organs by mistake. This is called autoimmune disease.

If antibodies attack your thyroid, they can cause serious thyroid autoimmune diseases:

• Hashimoto's disease, also known as Hashimoto's thyroiditis, is the most common cause of hypothyroidism (underactive thyroid). Hypothyroidism happens when your thyroid doesn't make enough thyroid hormones to meet your body's needs. Thyroid hormones affect the way your body uses energy. So, without enough thyroid hormones, many of your body's functions slow down.
• Graves' disease is the most common cause of hyperthyroidism (overactive thyroid). With hyperthyroidism, your thyroid makes more thyroid hormones than your body needs. This causes many of your body's functions to speed up.

If your health care provider has diagnosed you with hypothyroidism or hyperthyroidism, thyroid antibody tests can help find out if a thyroid autoimmune disease is causing the problem. There are different tests that check for different types of thyroid antibodies. Your provider will choose tests for you based on your symptoms, the results of other tests, and information about your medical history and family health history.

Other names: thyroid autoantibodies, thyroid peroxidase antibody, TPO, anti-TPO, antithyroid microsomal antibody, thyroid- stimulating immunoglobulin, TSI, TSH receptor antibody, Long-acting thyroid stimulator, LATS, TSH receptor-binding inhibitory immunoglobulin, Human thyroid stimulator

What is it used for?

If tests of your thyroid hormone levels show that your thyroid isn't working properly, your provider may order thyroid antibody tests to see if an autoimmune disease is causing the problem.

Thyroid antibody tests are used to check for different thyroid antibodies that affect your thyroid in different ways. These antibodies include:

• Thyroid peroxidase antibodies (TPOAb). High levels of these antibodies are a sign that Hashimoto's disease is causing hypothyroidism.
• Thyroglobulin antibodies (TgAb). High levels of these antibodies are a sign of Hashimoto's disease.
• Thyrotropin receptor antibodies (TRAb). These antibodies can be a sign of Graves' disease.

Why do I need a thyroid antibody test?

You may need a thyroid antibody test if you have symptoms of Hashimoto's disease or Graves' disease. But first, your provider will usually order blood tests to check your thyroid hormone levels to see if you have hyperthyroidism or hypothyroidism. Thyroid hormone tests include T3, T4, and TSH (thyroid-stimulating hormone).

Sometimes these test results, along with your health history, your family, an exam, and your symptoms, are enough to make a diagnosis with thyroid antibody testing.

Symptoms of Hashimoto's disease include:

• Weight gain
• Fatigue
• Hair loss
• Low tolerance for cold temperatures
• Irregular menstrual periods
• Constipation
• Depression
• Joint pain

Symptoms of Graves' disease include:

• Weight loss
• Bulging of the eyes
• Tremors in the hand
• Low tolerance for heat
• Trouble sleeping
• Anxiety
• Increased heart rate
• Swollen thyroid, known as goiter

What happens during a thyroid antibody test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

There are no special preparations necessary for a thyroid antibodies blood test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Your results may show one of the following:

• Negative: no thyroid antibodies were found. This means your thyroid symptoms are probably not caused by an autoimmune disease.
• Positive: thyroid antibodies, TPOAb and/or TgAb, were found. This may mean you have Hashimoto's disease. Most people with Hashimoto's disease have high levels of one or both of these types of antibodies.
• Positive: thyroid antibodies, TPOAb and/or TRAb, were found. This may mean you have Graves' disease.

The more thyroid antibodies you have, the more likely it is that you have an autoimmune disorder of the thyroid. If you are diagnosed with Hashimoto's disease or Graves' disease, there are medicines you can take to manage your condition.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a thyroid antibody test?

Thyroid disease can get worse during pregnancy. This can harm both the mother and her unborn baby. If you have ever had thyroid disease and are pregnant, you may be tested for thyroid antibodies along with tests that measure thyroid hormones. Medicines to treat thyroid disease are safe to take during pregnancy.