Anti-Thyroid Peroxidase Antibody (A-TPO) is an immunoassay assessing antibodies against thyroid peroxidase, an enzyme located on the thyroid cell surface that facilitates the iodination of thyroglobulin and produces thyroxine (T4) and triiodothyronine (T3). Antibodies against this enzyme lead to immunological insults to follicular cells, inflammatory damage, and autoimmune thyroid dysfunction. Monitoring its level helps healthcare providers predict the risk of hypothyroidism and guide early intervention.