Anti-Thyroglobulin Antibody (A-TG) is an immunoassay that detects specific antibodies against thyroglobulin, a protein produced by thyroid cells, stored in thyroid follicles involved in thyroid hormone synthesis, serves as a reservoir for thyroxine (T4) and triiodothyronine (T3). ATG is elevated in autoimmune thyroid disorders, commonly Hashimoto’s thyroiditis and Graves’ disease. The test helps healthcare professionals evaluate thyroid dysfunction, hormone level impairment, and therapeutic needs.