Thyroid peroxidase antibodiesTPO antibodies · Anti-TPO
Antibodies against a thyroid enzyme, marking autoimmune thyroid disease.
Thyroid peroxidase is an enzyme the thyroid uses to build its hormones. TPO antibodies are immune proteins directed against it, and their presence indicates the immune system is targeting thyroid tissue.
It matters because it explains a cause rather than measuring a level. Where thyroid function is abnormal, positive TPO antibodies point to autoimmune thyroid disease as the reason, most commonly Hashimoto's.
In practice a positive result can occur in people whose thyroid function is entirely normal, where it indicates raised risk rather than present disease, and the antibody level itself is not tracked as a measure of control.