Anti Thyroglobulin Antibodies

Function

Anti-Thyroglobulin (Anti-Tg) antibodies are autoantibodies produced by the immune system that mistakenly attack thyroglobulin, a protein found in the thyroid gland used to produce thyroid hormones. Under normal conditions, thyroglobulin remains within the thyroid follicles. However, if the thyroid is damaged by an autoimmune process, thyroglobulin may leak into the bloodstream, triggering the production of these antibodies.

Why it is Ordered

This test is primarily ordered to help diagnose autoimmune thyroid disorders. It is often requested alongside Anti-Thyroid Peroxidase (Anti-TPO) antibodies. Common reasons for ordering include investigating the cause of a goiter, evaluating symptoms of hypothyroidism or hyperthyroidism, and monitoring patients who have undergone treatment for differentiated thyroid cancer. In the context of thyroid cancer, Anti-Tg antibodies are monitored because their presence can interfere with thyroglobulin tests used to detect cancer recurrence.

Associated Conditions

• Hashimoto’s Thyroiditis: The most common cause of hypothyroidism in iodine-sufficient areas. High levels are found in 60-90% of patients.
• Graves’ Disease: An autoimmune cause of hyperthyroidism. About 30% of these patients test positive for Anti-Tg.
• Thyroid Cancer: While not a diagnostic tool for cancer itself, its levels are crucial for post-surgical follow-up.
• Other Autoimmune Disorders: Occasionally, levels may be elevated in individuals with Type 1 Diabetes or Rheumatoid Arthritis.

Summary

Monitoring Anti-Tg is essential for a complete thyroid profile. While a small percentage of the healthy population may have low levels of these antibodies, high titers almost always indicate an underlying autoimmune response that requires clinical correlation with TSH and Free T4 levels.