Test Details: Thyroid antibodies develop when a person’s immune system mistakenly targets components of the thyroid gland as foreign body. This autoimmune response, in which the immune system mistakenly damages tissues in the body, can lead to chronic inflammation of the thyroid, tissue damage and/or disruption of thyroid function. This test is used to diagnose an autoimmune disorder, such as Hashimoto’s thyroiditis or Graves’ disease. Thyroid peroxidase (TPO) is an enzyme that is crucial to the production of thyroid hormones. TPO Antibody may interfere with the action of this enzyme. Almost all patients with Hashimoto’s thyroiditis have high levels of TPO Antibody.