Thyroid peroxidase is a type of protein (called an enzyme) that cells in the thyroid gland use to make thyroid hormone. If these enzymes leak out into the bloodstream (as when thyroid cells are damaged) the immune system makes antibodies against these proteins. The thyroid peroxidase antibody test measures these antibodies in the blood.
How the Test is Performed
A blood sample is needed.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
Why the Test is Performed
This test is done to confirm the cause of thyroid problems, including Hashimoto thyroiditis.
The test is also used to find out if an immune or autoimmune disorder is damaging the thyroid.
Normal Results
A negative test means the result is normal.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens. Talk to your health care provider about the meaning of your specific test results.
What Abnormal Results Mean
A positive test may be due to:
- Granulomatous or subacute thyroiditis (an immune reaction of the thyroid gland that often follows an upper respiratory infection)
- Hashimoto thyroiditis (a reaction of the immune system against the thyroid gland)
High levels of these antibodies have also been linked with an increased risk of:
- Miscarriage
- Preeclampsia (high blood pressure and protein in the urine after the 20th week of pregnancy)
- Premature birth
- In vitro fertilization failure
Important: A positive result does not always mean that you have a thyroid condition or that you need treatment for your thyroid. A positive result may mean that you have a higher chance of developing thyroid disease in the future. This is often associated with a family history of thyroid disease.
Antithyroid microsomal antibodies may be seen in your blood if you have other autoimmune conditions, including:
- Autoimmune hemolytic anemia
- Autoimmune hepatitis
- Autoimmune adrenal disease
- Rheumatoid arthritis
- Sjögren syndrome
- Systemic lupus erythematosus