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What is thyroid peroxidase?
Thyroid peroxidase (TPO) is an enzyme made in the thyroid gland that is important in the production of thyroid hormone. TPO is found in thyroid follicle cells where it converts the thyroid hormone T4 to T3.
The thyroid gland is located in the lower part of the neck, below the Adam's apple, wrapped around the trachea (windpipe).
What is the thyroid peroxidase test?
Thyroid peroxidase test is a test that measures the level of an antibody that is directed against thyroid peroxidase (TPO).
Autoantibodies to thyroid peroxidase (TPOAb) are produced within the body. The presence of TPOAb in the blood reflects a prior attack on the thyroid tissue by the body's immune system.
What does a positive thyroid peroxidase test mean?
- Most people with chronic thyroiditis display a positive TPO test. The test is also positive in lesser numbers of people with other thyroid diseases.
- Other autoimmune disorders that may cause a positive TPOAb test include:
- About 3% of people with a positive TPOAb test show no evidence of disease.
- The chance of having a positive TPOAb test is greater in females and increases with age.
What are other names for thyroid peroxidase test?
This test goes by a confusing number of names, including:
- thyroid peroxidase (TPO) antibody (TPOAb) test,
- thyroid peroxidase autoantibody test,
- antimicrosomal antibody test, and
- antithyroid microsomal antibody test.
Previous contributing author: Frederick Hecht, MD, FAAP
Medically reviewed by John A. Seibel, MD; Board Certified Internal Medicine with a subspecialty in Endocrinology & Metabolism
"Laboratory assessment of thyroid function"