TPO antibodies
Antibodies targeting thyroid peroxidase - the main marker of Hashimoto's thyroiditis, also raised in Graves' disease.
TPO antibodies (anti-thyroid peroxidase antibodies) are produced by the immune system against thyroid peroxidase - an enzyme the thyroid uses to make T4 and T3.
Elevated TPO antibodies are the hallmark of Hashimoto's thyroiditis and are found in up to 95% of people with this condition. They are also raised in around 50 - 80% of people with Graves' disease.
TPO antibodies are commonly measured when: hypothyroidism is diagnosed (to check whether it is autoimmune in origin); TSH is mildly raised and the cause is unclear; thyroid symptoms are present but TSH is normal; or a goitre is found.
A positive TPO result does not always mean thyroid function is abnormal now. However, it indicates that the autoimmune process is present and regular monitoring is sensible. The level of TPO antibodies does not reliably indicate how much thyroid damage has occurred or how quickly function will change.
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