The Anti-TPO (Thyroid Peroxidase) Antibody test measures the level of antibodies against thyroid peroxidase, an enzyme essential for the production of thyroid hormones. Elevated levels of these antibodies are commonly associated with autoimmune thyroid diseases, such as Hashimoto’s thyroiditis (leading to hypothyroidism) and Graves’ disease (leading to hyperthyroidism). This test is useful for diagnosing thyroid disorders, particularly when symptoms suggest an autoimmune cause. A blood sample is required for this test.