What can a TPOAb test tell you?
A TPOAb test helps healthcare providers determine whether the immune system is attacking the thyroid and causing inflammation or damage. When TPOAb levels are high, this indicates an autoimmune response that typically leads to hypothyroidism, although it may occasionally appear in hyperthyroid states such as Graves’ disease. This shift from TSH receptor antibodies to TPOAb has been documented in patients transitioning from hyperthyroidism to hypothyroidism, supporting the link between rising TPOAb levels and thyroid failure.
Providers commonly order this test to:
Evaluate the cause of abnormal thyroid function tests (TSH and free T4)
Diagnose or confirm Hashimoto’s thyroiditis in patients with hypothyroid symptoms
Support a diagnosis of Graves’ disease in patients with hyperthyroidism
Assess autoimmune risk in people with other autoimmune conditions (e.g., type 1 diabetes, celiac disease)
Monitor antibody trends over time if autoimmune thyroid disease is known
Even if thyroid hormone levels are normal, a positive TPOAb test may signal increased risk for future thyroid dysfunction.
What is being tested?
Thyroid peroxidase (TPO) is an enzyme anchored on the surface of thyroid cells. It catalyzes key steps in thyroid hormone synthesis, including binding iodine to tyrosine molecules in thyroglobulin to form T3 and T4.
TPO antibodies are immunoglobulin G (IgG) autoantibodies that develop when the immune system mistakenly targets this enzyme as foreign. High levels reflect thyroid inflammation that can lead to thyroid failure (typical of Hashimoto’s disease). They are also detectable in many people with Graves’ disease and in some without clinical thyroid symptoms.
Where is the TPOAb test typically included?
The TPOAb test is usually part of a thyroid antibody panel, often combined with:
Thyroglobulin antibodies, to evaluate broader autoimmune activity
TSH, free T4, and free T3 to measure thyroid function
Providers may order a TPO antibody test if your thyroid levels are low or borderline and they want to see whether an autoimmune condition like Hashimoto’s is to blame. Once diagnosed, though, repeat testing usually isn’t needed — it won’t change your treatment, but it can help you better understand your thyroid condition.
Who should get a TPOAb test?
Healthcare providers may recommend a TPOAb test if you have abnormal TSH or T4 test results or symptoms of thyroid dysfunction or autoimmune disease.
Common symptoms that may prompt testing include:
