Ajax Harwood Clinic

Thyroid antibody test (TPOAb)

Full name: Thyroid peroxidase antibodies (TPOAb)

This test is useful only in specific situations — it's not right for everyone who asks about it.

What this test is

TPO antibodies show if your immune system is attacking your thyroid. This is called Hashimoto's disease. Your immune system can attack the thyroid for years before TSH changes. Checking TPO antibodies helps once your TSH is already abnormal. It also helps if TSH is only mildly high, to decide whether to treat or just watch it. This matters more if you are planning a pregnancy. A positive result does not mean your thyroid is failing right now. About one in ten healthy adults has positive TPO antibodies and never gets thyroid disease. If your TSH is normal, a positive result mainly means watching your thyroid over time.

Want to see the full clinical reasoning? The reference we use for this test is open to anyone — it is detailed and written for clinicians, and you are welcome to read it.

Open the clinician reference →

Looking for other tests, or more on a condition an ND raised? Explore ask.ajaxharwoodclinic.com →

General health information for Ajax Harwood Clinic patients and the public — not medical advice, and not a substitute for seeing your own doctor. Last reviewed 2026-09-24.