Antibody, antithyroglobulin: An antibody directed against thyroglobulin which is a key protein in the thyroid gland essential to the production of thyroid hormones (thyroxine and triiodothyronine). Antithyroglobulin antibodies can damage the thyroid gland and affect its function.

Testing for antithyroglobulin antibodies in the blood is useful in the diagnosis of some thyroid and other disorders. Conditions in which there may be antithyroglobulin antibodies include: Hashimoto thyroiditis (an autoimmune thyroid disease), Graves disease (overactivity of the thyroid), hypothyroidism (underactivity of the thyroid), thyroid cancer, lupus, rheumatoid arthritis, autoimmune hemolytic anemia and Sjogren syndrome.

Antithyroglobulin antibodies are also called antithyroid antibodies.