Blood Test: Thyroid Peroxidase Antibodies

What Is a Blood Test?

By taking and testing a small sample of a person’s blood, doctors can check for many kinds of diseases and conditions. Blood tests help doctors check how the body’s organs are working and see if medical treatments are helpful.

To help your child get ready for a blood test, find out if they need to fast (not eat or drink) or should stop taking medicines before the test. Explain what to expect during the test. If your child is anxious about it, work together on ways to stay calm.

What Are Thyroid Peroxidase Antibodies?

Thyroid peroxidase (TPO) is an enzyme made by the thyroid gland. The thyroid uses iodine, with the help of TPO, to make the hormones triiodothyronine (T3) and thyroxine (T4). These both help control metabolism and growth.

A thyroid peroxidase antibodies test checks for antibodies made against the TPO. Antibodies (also called immunoglobulins) are proteins the immune system makes to recognize and get rid of germs. Usually, the immune system doesn't make a lot of antibodies against thyroid peroxidase because it's not a germ.

In autoimmune disorders, the immune system attacks the body's healthy tissues as though they were foreign invaders, like germs. So the level of TPO antibodies in blood may rise in people with a thyroid-related autoimmune condition.

Why Are Thyroid Peroxidase Antibodies Tests Done?

Doctors order thyroid peroxidase antibodies tests:

to diagnose and monitor autoimmune conditions involving the thyroid, such as Hashimoto's thyroiditis and Graves’ disease
to diagnose thyroid disorders such as thyroiditis (inflammation of the thyroid) or goiter (an enlarged thyroid)
if other blood tests to check levels of thyroid hormones or thyroid stimulating hormone (TSH) show a problem