THYROGLOBULIN ANTIBODY - A serologic blood test which measures the antithyroglobulin antibodies in the blood. Thyroglobulin is a protein found in thyroid tissue. It is the source of thyroid hormones in the body. The presence of antibodies to this protein can result in decreased thyroid gland function. A negative assay is considered normal. Conditions where the assay may be positive include: lupus, rheumatoid arthritis, Hashimoto's thyroiditis, thyrotoxicosis, hypothyroidism, thyroid cancer, myxedema, Sjogren's syndrome, and autoimmune hemolytic anemia.