TPO antibodies (thyroperoxidase antibodies) are antibodies that are formed against the enzyme thyroperoxidase (TPO) in the thyroid gland. TPO is an enzyme responsible for converting iodine into the hormones thyroxine (T4) and triiodothyronine (T3).
TPO antibodies are analyzed to identify if there is any autoimmune disease in the thyroid gland, such as Hashimoto's thyroiditis. This disease causes damage to thyroid cells and reduced production of hormones.