Thyroid Peroxidase Antibodies (TPO)

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.

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. Thyroid peroxidase antibodies (TPO) in particular are linked with autoimmune thyroid conditions such as Hashimoto's disease and Graves' disease, and they can also be raised in goiter and in other autoimmune disorders such as Addison's disease and type 1 (insulin-dependent) diabetes. 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.

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.

TPO antibodies are positive in roughly 90% of people with Hashimoto's disease and in many people with Graves' disease. Low-level positives can also be seen in about 10% of healthy people, especially women.

If you have a slightly high TSH (subclinical hypothyroidism) and a positive TPO antibody result, you have a higher chance of developing full hypothyroidism over time. This can affect whether your provider chooses to start thyroid hormone treatment.

Higher TPO antibody levels are most often seen with autoimmune thyroid conditions, but can sometimes appear in people with other related autoimmune disorders. Your provider will look at your antibody results together with thyroid hormone tests and your symptoms.