TPO Antibodies

Function

Thyroid Peroxidase (TPO) is an enzyme normally found in the thyroid gland that plays a crucial role in the production of thyroid hormones (T3 and T4). TPO Antibodies (anti-TPO) are autoantibodies produced by the immune system that mistakenly attack the thyroid gland. The presence of these antibodies indicates an autoimmune process where the body is targeting its own endocrine tissue.

Why it is Ordered

Physicians order the TPO antibody test primarily to diagnose autoimmune thyroid disorders. It is indicated when:

• TSH levels are abnormal but T3/T4 are borderline.
• A patient has symptoms of hypothyroidism (fatigue, weight gain, cold intolerance) or hyperthyroidism.
• A goiter (enlarged thyroid) is detected during a physical exam.
• Evaluating the risk of thyroid dysfunction in pregnant women with other autoimmune conditions.

Associated Conditions

The most significant association is with Hashimoto's Thyroiditis, the leading cause of hypothyroidism in iodine-sufficient regions; over 90% of these patients test positive. It is also found in about 75% of patients with Graves' Disease (hyperthyroidism). Beyond thyroid-specific issues, positive TPO antibodies can sometimes be found in patients with other autoimmune diseases like Type 1 Diabetes, Rheumatoid Arthritis, or Pernicious Anemia. Interestingly, a small percentage of the healthy population may have low levels of these antibodies without developing clinical disease, though they remain at higher risk for future thyroid issues.