Thyroid peroxidase antibodies (anti-TPO)

Thyroid peroxidase antibodies (anti-TPO) are autoantibodies directed against thyroid peroxidase, an enzyme essential for the production of thyroid hormones. This test measures the level of these antibodies in a simple blood sample and is used to investigate autoimmune thyroid disease. It is particularly valuable for anyone with an unexplained underactive or overactive thyroid, a family history of thyroid autoimmunity, or symptoms such as fatigue, weight change, hair thinning, or neck discomfort.

The test is analysed using a validated immunoassay technique, which provides a reliable and reproducible measurement of anti-TPO levels. Raised concentrations suggest that the immune system is targeting the thyroid gland and can support the diagnosis of conditions such as Hashimoto's thyroiditis or Graves' disease. It is often requested alongside thyroid function tests (TSH, free T4, and free T3) to give a complete picture of thyroid health.

Biomarkers included

• Anti-thyroid peroxidase antibodies (anti-TPO)

Why it matters

Anti-TPO is the most sensitive serological marker for autoimmune thyroid disease. Identifying it helps explain abnormal thyroid function, guides monitoring, and informs treatment decisions. For many people, it provides the missing piece in understanding persistent symptoms and allows for earlier, more targeted management.