Diseases

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

• 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:
  • Sjogren's syndrome,
  • lupus,
  • rheumatoid arthritis, and
  • pernicious anemia.
• 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.

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.

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). Picture of the thyroid gland