Blood Test: Thyroid Peroxidase Antibodies

What It Is

A thyroid peroxidase antibodies test checks the levels of antibodies made against the compound thyroid peroxidase (TPO) in the bloodstream. Thyroid peroxidase is an enzyme produced by the thyroid gland. The thyroid is a small, butterfly-shaped gland in the neck that uses iodine to create the hormones triiodothyronine (T3) and thyroxine (T4), both of which help control metabolism and growth. Antibodies are proteins made by the immune system, usually to fight bacteria, viruses, and toxins that enter or contact the body.

Ordinarily, a healthy immune system doesn't make significant levels of antibodies against thyroid peroxidase, because it's not "foreign," but rather a necessary component of thyroid tissue.

In autoimmune diseases, however, the immune system malfunctions, mistakenly attacking healthy organs and tissues as though they were foreign invaders. In people with a thyroid-related autoimmune condition, the blood level of TPO antibodies may rise.

Why It's Done

The thyroid peroxidase antibodies test is primarily used to help diagnose and monitor autoimmune conditions involving the thyroid gland, such as Hashimoto's thyroiditis and Graves disease.

The test may be ordered when a child has symptoms of a thyroid disorder, including thyroiditis (inflammation of the thyroid) or goiter (an enlarged thyroid), or if tests to check thyroid gland function, such as levels of thyroid hormones or thyroid stimulating hormone (TSH), show abnormalities.



The Procedure


After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting the blood for the test will only take a few minutes. Collecting blood for this test will only take a few minutes.


What to Expect


Getting the Results

The blood sample will be processed by a machine. The results are commonly available after a few days.



  • fainting or feeling lightheaded
  • pain associated with multiple punctures to locate a vein

Helping Your Child



If You Have Questions

If you have questions about the thyroid peroxidase antibodies test, speak with your doctor. You can also talk to the technician before the procedure.

Reviewed by: Steven Dowshen, MD
Date reviewed: April 2011

Kids Health

