Thyroid Antibodies (Thyroid Peroxidase Antibody)

General Information

Anti-thyroid peroxidise (TPO) antibodies are autoantibodies directed against the thyroid peroxidise enzyme. This enzyme catalyses the iodination of tyrosine in thyroglobulin during the biosynthesis of T3 and T4. The two most common forms of autoimmune thyroid disease are Hashimoto's thyroiditis and Grave's disease. High anti-TPO antibodies are present in up to 90% of patients with Hashimoto's thyroiditis. They are also present in more than 70% of patients with Grave's disease. A negative finding does not rule out the possibility of an autimmune disease and the magnitude of the antibody titre does not correlate with the clinical activity of the disease.

Note that TPO antibodies may also be detected, to variable degrees, in patients with other organ-specific autoimmune diseases, and also to a lesser extent in the normal population. This test is only of real value in the diagnosis of autoimmune thyroid disease, as levels of TPO antibodies do not correlate well with thyroid functional status.