Thyroid peroxidase (TPO) is an enzyme that plays an important role in the synthesis of thyroid hormones (thyroxine – T4 and triiodothyronine – T3). An autoantibody produced against it (anti-TPO) can interfere with the synthesis of hormones (T4 and T3), but in many cases it is asymptomatic. Its importance is in the diagnosis of autoimmune thyroid disease.

The laboratory test detects the amount of anti-thyroid peroxidase autoantibody in the blood.

Anti-TPO testing is recommended in all cases where TSH, T4 and T3 levels are abnormal. The result of the test can help to determine the cause of the thyroid dysfunction and to design the appropriate medication.

Determination of anti-TPO levels may also be necessary in pregnancy, especially when there is a diagnosis of autoimmune disease (e.g. Hashimoto’s or Graves-Basedow disease).

The test requires a blood sample taken from a vein.

A high anti-TPO level means that the body is producing antibodies against the important thyroid enzyme TPO. This is an autoimmune process and with appropriate medication, a symptom-free condition can be achieved.

The test alone does not diagnose any disease, and you should always consult an endocrinologist with the results to determine the exact diagnosis and the necessary therapy.