Thyroid antibodies

Thyroid antibodies are proteins produced by the immune system that mistakenly attack components of the thyroid gland or its signalling system. Their presence in the blood is a marker of autoimmune thyroid disease.

The two antibodies most commonly tested are TPO antibodies (anti-thyroid peroxidase) - raised in Hashimoto's thyroiditis and, to a lesser degree, in Graves' disease - and TRAb (TSH receptor antibodies) - specific to Graves' disease, where they drive overproduction of thyroid hormone.

A smaller number of people have elevated thyroglobulin antibodies (anti-Tg), which can also indicate autoimmune thyroid disease and may interfere with thyroglobulin monitoring after thyroid cancer treatment.

Having positive antibodies does not necessarily mean thyroid dysfunction is present now or will develop. Many people with mildly raised TPO antibodies have normal thyroid function for years. However, raised antibodies do indicate an increased risk of developing dysfunction, so regular monitoring is usually recommended.