The Anti-Thyroid Peroxidase Antibodies (Anti-TPO or TPO) test is a blood test used to measure the levels of antibodies produced against thyroid peroxidase, an enzyme essential for the production of thyroid hormones. These antibodies promote an immune response against the thyroid gland, leading to inflammation and dysfunction. This test is a key tool in diagnosing autoimmune thyroid diseases, such as Hashimoto's disease, which can result in hypothyroidism. Elevated levels of these antibodies indicate abnormal immune activity that can affect hormone production. The TPO test is often used alongside other tests to assess thyroid health, helping doctors develop an appropriate treatment plan and effectively monitor the patient's condition.