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Definition of Thyroid peroxidase test

Reviewed on 3/29/2021

Thyroid peroxidase test: A blood test done to detect autoantibodies directed against thyroid peroxidase (TPO), an enzyme in the thyroid gland that is very important to the production of thyroid hormones. TPO is found in thyroid follicle cells where it catalyzes the iodination of T4 and T3 in the biosynthesis of thyroid hormones.

Autoantibodies to thyroid peroxidase (abbreviated TPOAb) are produced by the body itself. TPOAb can attack the thyroid and damage thyroid function. These antibodies are present in a high proportion (70% to 90%) of people with chronic thyroiditis. These antibodies are also present in lesser numbers of people with other thyroid diseases. Other autoimmune disorders such as Sjogren syndrome, lupus, rheumatoid arthritis, and pernicious anemia are sometimes positive for TPOAb. Small numbers (around 3%) of people may have TPOAb show no evidence of disease. The chance of having TPOAb is greater in females and increases with age.

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.


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