Thyroid Peroxidase Antibodies

Test Quick Guide

Thyroid antibodies develop when your immune system mistakenly targets components of the thyroid gland or proteins. This autoimmune response, in which the immune system mistakenly damages tissues in the body, can lead to chronic thyroid inflammation, tissue damage, and/or disruption of thyroid function.

Laboratory tests detect the presence and measure the quantity of specific thyroid antibodies in the blood. Understanding the underlying cause of thyroid dysfunction can help doctors plan the best course of treatment.

About the Test

Purpose of the test

Thyroid antibody tests are used in diagnosing hypothyroidism or hyperthyroidism as a result of autoimmune thyroid disease. Hypothyroidism describes an underactive thyroid gland, while hyperthyroidism is an overactive thyroid gland. Thyroid antibody tests may also be used for the following purposes:

  • To diagnose an autoimmune disorder, such as Hashimoto’s thyroiditis or Graves’ disease
  • To define the best course of treatment
  • To determine whether your mild hypothyroidism is likely to get worse over time
  • To evaluate the risk to the fetus in pregnant individuals with thyroid disease
  • To estimate the risk of relapse after treatment for Graves’ disease
  • To monitor if you have been previously treated for thyroid cancer

In the U.S., most cases of hypothyroidism occur in Hashimoto’s thyroiditis, which affects women five to 10 times more frequently than men. Hyperthyroidism is caused by another autoimmune disease called Graves’ disease — women are more susceptible to this, especially in the fifth and sixth decades of life.

In both cases, the immune system interferes with the normal functioning of the thyroid gland. Hashimoto’s thyroiditis is so common in the U.S. that it is often assumed to cause an underactive thyroid.

Although detecting thyroid antibodies can support a diagnosis of Graves’ disease or Hashimoto’s thyroiditis, it is not always necessary to test thyroid antibodies to diagnose other autoimmune disorders.

What does the test measure?

The thyroid produces thyroglobulin — a protein critical to the production of T3 (triiodothyronine) and T4 (thyroxine) hormones — which circulates in the blood in free (FT3 and FT4) and bound forms. Also, the pituitary gland releases another hormone into the blood, called thyroid-stimulating hormone (TSH, also known as thyrotropin), to stimulate more thyroid hormone production.

Thyroid peroxidase (TPO) is an enzyme also stimulated by TSH. While levels of these hormones can be measured, abnormally high or low levels of T4 and FSH generally provide the first clue of a thyroid problem and are considered the best tests to measure thyroid status.

When an autoimmune problem is thought to cause a thyroid abnormality, thyroid antibody testing is performed. The testing detects and measures the levels of thyroid antibodies in the blood.

Normally, antibodies attack foreign substances in the body, like bacteria, viruses, parasites, and toxins. If you have autoimmune disorders, antibodies mistakenly target the body’s tissues.

These antibodies attacking your body are also known as autoantibodies or antithyroid antibodies. Thyroid antibody testing may look for several types of thyroid antibodies:

  • Thyroid peroxidase antibodies (TPOAb): This is an enzyme crucial to producing thyroid hormones. TPOAb may interfere with the action of this enzyme. Almost all patients with Hashimoto’s thyroiditis have high levels of TPOAb.
  • Thyroglobulin antibodies (TgAb): This may be present when the thyroid has been damaged. These antibodies are often measured in addition to thyroglobulin tests after you complete treatment for thyroid cancer.
  • Thyrotropin receptor antibodies (TRAb): These antibodies bind to the receptors on thyroid cells normally activated by TSH. In Graves’ disease, an antibody called thyroid-stimulating immunoglobulin (TSI) binds to the TSH receptor and mimics the action of TSH. This causes constant stimulation of the thyroid gland, prompting it to release too much thyroid hormone.

When should I get a thyroid antibody test?

It is not always necessary to test for thyroid antibodies to establish a diagnosis of an autoimmune disorder affecting the thyroid. Yet doctors may find thyroid antibody testing helpful in the following situations:

  • Subclinical hypothyroidism: If you have a high TSH and a normal FT4, testing for TPO antibodies may help predict whether the hypothyroidism will progress from being subclinical — in which it may not cause significant or observable symptoms — to more severe and permanent dysfunction.
  • Goiter: This is the abnormal enlargement of the thyroid gland. Some experts recommend testing for TPOAb if you have a goiter, even if your thyroid hormone levels are normal.
  • Hyperthyroidism, if the cause is not obvious: If you have an overactive thyroid, sometimes it is clear from your physical examination and thyroid hormone tests that you have Graves’ disease. In less obvious cases, TRAb testing or imaging tests, such as ultrasound or radionuclide thyroid scan, may help diagnose or rule out Graves’ disease.
  • Monitoring after thyroid cancer treatment: If you are monitored with thyroglobulin testing after treatment, you may also have your TgAb levels tested, as they can interfere with some thyroglobulin tests.

Although thyroglobulin antibodies may be elevated in both Hashimoto’s thyroiditisand Graves’ disease, it is not typically tested during diagnosis.

Common symptoms for Hashimoto’s thyroiditis:

  • Weight gain
  • Fatigue
  • Hair loss
  • Low tolerance to cold
  • Depression
  • Joint pain

Common symptoms for Graves’ disease:

  • Weight loss
  • Bulging eyes
  • Tremors
  • Low tolerance to heat
  • Anxiety
  • Swollen thyroid (goiter)

Finding a Thyroid Antibodies Test

How can I get a thyroid antibodies test?

A doctor typically orders thyroid antibody tests after other blood tests suggest a potential thyroid disorder. They use a blood sample for testing, which can be taken at a doctor’s office, clinic, lab, hospital, or another medical setting.

Can I take the test at home?

Test kits allow you to test for certain thyroid antibodies at home. These kits provide the supplies needed for obtaining a blood sample and returning it to the company for analysis.

Some kits include one or more thyroid antibody tests as part of a panel of thyroid tests, while others test only for TPOAb or TgAb. At-home tests for TRAb may not be commercially available at this time.

Thyroid antibody tests are difficult to interpret and may be unnecessary if other thyroid tests are normal. If an abnormal level of thyroid antibodies is detected on an at-home thyroid test, an endocrinologist will likely want the test to be repeated.

How much does the test cost?

Thyroid antibody test costs vary based on factors such as where the test is done, whether or not you have health care coverage, how many antibodies are tested for, and whether other tests are performed along with the antibodies one. A thyroid peroxidase antibodies test kit costs $89 from Testing.com.

When ordered by a doctor, insurance typically covers the test, although you may have to pay a deductible or co-pay. Your doctor’s office, lab, and health plan can provide information about any out-of-pocket costs that may be your responsibility.

Taking a Thyroid Antibodies Test

Thyroid antibody tests require a sample of blood. You may have blood drawn from your arm at a doctor’s office, clinic, laboratory, hospital, or another medical setting.

Before the test

No special preparation is required for a thyroid antibodies blood test. If you have thyroid function tests such as TSH, T3, or T4 at the same time as the antibodies test, be sure to tell your doctor about any medications or supplements you are taking.

During the test

To obtain a blood sample, a needle is inserted into a vein in your arm. Before your sample is drawn, an elastic band is tied around your upper arm to increase blood in the veins of your arm and make it easier to extract a sample. The skin at the puncture location is cleaned with an antiseptic. You will probably feel a slight sting when the needle enters your skin. The blood draw typically takes less than a minute.

After the test

After a blood sample has been taken, a bandage or cotton swab will be placed over the puncture site to prevent bleeding. You will likely be instructed to keep the bandage or swab in place for an hour or more.

You may resume your normal activities, including driving, after giving a blood sample.

Thyroid Antibodies Test Results

Receiving test results

Thyroid antibody test results are usually available within several days after your blood draw. Your doctor’s office may contact you to share results over the phone or to schedule an appointment to discuss them. You may also receive test results through an online patient portal or by mail.

Interpreting test results

If your results indicate you have abnormal levels of thyroid antibodies, it may be an indication of an autoimmune disorder. Thyroid antibody tests can be complex to interpret, and normal results can vary slightly between different laboratories. It is important to discuss the significance of your test results with a doctor or a specialist. The reference ranges below are from the American Board of Internal Medicine:

Thyroid peroxidase antibodies (TPOAb): If you are diagnosed with hypothyroidism, you may have a TPOAb test. A TPO antibody test may be done if you have a high TSH to determine the cause. Elevated TPO is usually indicative of hypothyroidism as seen in Hashimoto’s thyroiditis.

TPO antibodies are present in more than 90% of patients with hypothyroidism and 10% who do not have a thyroid problem yet may develop a future autoimmune problem. These antibodies are almost always high in 95% of patients with Hashimoto’s thyroiditis and 70% of those with Graves’ disease. But even if you don’t have symptoms of thyroid disease, you may also have TPO antibodies.

Thyroglobulin antibodies (TgAb): Although this is usually elevated if you have autoimmune thyroid disorders, it is not usually tested if you have Hashimoto’s thyroiditis and Graves’ disease. Thyroglobulin antibodies may be tested to monitor thyroid cancer after treatment.

Thyrotropin receptor antibodies (TRAb): This autoantibody inhibits proper TSH activity. Two types of autoantibodies prevent normal TSH function. TSI binds to thyroid receptors, blocking TSH activity yet promoting increased thyroid hormone production, creating hyperthyroidism. Thyroid-binding inhibitory immunoglobulin (TBII) blocks TSH from binding, resulting in hyperthyroidism. Discuss the reference ranges for TRAbs with your physician.

If you have Graves’ disease, you will usually have abnormal levels of antibodies that stimulate the thyroid gland. Although not all patients with Graves’ disease have detectable levels of antibodies, a positive thyroid-stimulating receptor antibody test result is considered diagnostic for Graves’ disease.

You may find it helpful to ask your physician the following questions about your test results:

  • Were my results positive for the presence of thyroid antibodies?
  • Do my results reveal the underlying cause of my thyroid disease?
  • Do my thyroid antibody results show what treatment would be most helpful for me?

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