What Are Thyroid Antibodies in a Blood Test?

Thyroid antibodies are immune proteins produced when the immune system attacks the thyroid gland. Testing helps diagnose autoimmune thyroid disease.

Anti-TPO (Anti-Thyroid Peroxidase)

• Associated with Hashimoto’s thyroiditis
• Present in 90–95% of Hashimoto’s patients
• Also found in 10–15% of healthy people
• Higher levels = faster progression to hypothyroidism

TSI (Thyroid-Stimulating Immunoglobulin)

• Associated with Graves’ disease
• Stimulates thyroid to produce excess hormone
• Present in 90% of Graves’ patients
• Can cross placenta in pregnancy

Anti-Thyroglobulin (Anti-Tg)

• Often present alongside anti-TPO in Hashimoto’s
• Also used for thyroid cancer monitoring

When Are They Ordered?

• Elevated TSH with Hashimoto’s symptoms
• Family history of autoimmune thyroid disease
• Suspected Graves’ disease
• Before starting lithium or amiodarone
• Recurrent miscarriage or infertility

Important

• Positive antibodies confirm autoimmune etiology but do not require treatment by themselves — treatment is based on TSH and free T4