Thyroid Antibody Test

What is a thyroid antibody test?

A thyroid antibody test measures the level of thyroid antibodies in a sample of your blood to check for an autoimmune thyroid disease. 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 germs that could make you sick, such as viruses and bacteria. But sometimes antibodies attack your own healthy tissue and organs, believing them to be foreign substances. These antibodies are called autoantibodies, and your body makes them by mistake. If you have autoantibodies in your blood, it could be a sign of autoimmune disease.

There are many different types of autoantibodies, and they can affect your body in different ways. Some affect many different parts of your body while others affect only a specific organ. Thyroid antibodies are a type of autoantibody that affect your thyroid's ability to make healthy amounts of thyroid hormones, which affect the way your body uses energy. This can then cause serious autoimmune thyroid diseases such as:

• Hashimoto's disease, also known as Hashimoto's thyroiditis, which is the most common cause of hypothyroidism (underactive thyroid). With hypothyroidism, your thyroid doesn't make enough thyroid hormones to meet your body's needs. This causes many of your body 's functions to slow down.
• Graves' disease, which 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.

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?

Your provider may use thyroid antibody tests if other tests have shown that you have hypothyroidism or hyperthyroidism. These tests usually look for T3, T4, and TSH (thyroid-stimulating hormone). If any of these tests come back with results that show your levels are too high or too low, your provider may then use thyroid antibody tests to see if an autoimmune disease is causing the problem.

There are different tests that check for various types of thyroid antibodies. These antibodies each target different proteins that help your thyroid make hormones. These antibodies include:

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

Your provider will decide which tests to use based on your symptoms, the results of other tests, and information about your medical and family health histories.

Your provider can also use thyroid antibody tests to screen for autoimmune thyroid diseases if other thyroid tests have come back with results that are too high or too low and you have a high risk for an autoimmune thyroid condition. You may have a higher risk if you:

• Are female
• Are over the age of 50
• Have a family history of thyroid diseases such as Graves' disease or Hashimoto's disease
• Have other autoimmune conditions
• Have had thyroid surgery
• Have had radiation treatment to your neck
• Use medicines with a lot of iodine in them

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 and have thyroid hormone test results that suggest hyperthyroidism or hypothyroidism.

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

You may also need thyroid antibody testing if:

• You've had thyroid cancer treatment, and your provider wants to see if the cancer comes back
• You're pregnant and have thyroid disease or symptoms of thyroid disease

If you are pregnant, thyroid disease can harm both you and your fetus. So, it's important to get tested as soon as you know you're pregnant. This way, if you do have a thyroid disease, you can treat it as soon as possible. Medicines to treat thyroid disease are safe to take during pregnancy.

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 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, TSI, or TRAb, were found. This may mean you have Graves' disease or Hashimoto's 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.