Anti-TPO (Thyroid Peroxidase Antibodies) levels, explained
Anti-TPO antibodies are immune proteins directed against an enzyme inside the thyroid — their presence shows the immune system is attacking the gland.
What’s a normal Anti-TPO level?
Typical adult reference range, shown for orientation. Your report’s range may differ by lab, age, and sex — the analyzer uses your report’s own ranges when available.
What high and low Anti-TPO mean
A value outside the reference range is a flag, not a diagnosis. Here’s what each direction usually points to — and the most common causes.
High anti-TPO means autoimmune thyroid disease is present or developing — most often Hashimoto’s, which can slowly push the thyroid towards underactivity, even while TSH is still normal.
- Hashimoto’s (autoimmune) thyroiditis
- Graves’ disease
- Postpartum or silent thyroiditis
- Other autoimmune conditions (type 1 diabetes, celiac disease, pernicious anemia) and some medications (amiodarone, lithium, interferon)
A low or negative anti-TPO is the expected result — no evidence of thyroid autoimmunity.
- No autoimmune activity against the thyroid (the normal state)
- Rarely, autoimmune disease with antibodies against thyroglobulin instead
When a Anti-TPO result needs attention
Positive antibodies with a normal TSH do not need treatment but do justify checking thyroid function every 6–12 months, and before or during pregnancy. Positive antibodies with a raised TSH, symptoms of an under- or overactive thyroid, or a growing goitre should be reviewed by a clinician.
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Anti-TPO (Thyroid Peroxidase Antibodies) — frequently asked questions
- What does a high anti-TPO mean if my TSH is normal?
- That your immune system is reacting against your thyroid, but the gland is still keeping up. About 2–4% of such people develop an underactive thyroid each year, more if TSH is at the upper end of normal. Nothing needs treating now, but TSH should be checked periodically — and before conceiving, because thyroid autoimmunity raises the risk of miscarriage and postpartum thyroiditis.
- Can anti-TPO antibodies go down?
- They can fall over years, particularly with selenium supplementation in deficient people, after treatment of an overactive thyroid, or spontaneously, but they rarely disappear and the level does not track symptoms closely. Treatment decisions are based on TSH and how you feel, not on the antibody number.
- What is a normal anti-TPO level?
- Cut-offs are assay-specific: many labs use under 34 IU/mL, others under 9 or under 60. A result just above the cut-off is weakly positive and may be rechecked; levels in the hundreds or thousands are unequivocally positive. Always compare with the reference range printed on your own report.
Related lab markers
- TSH (Thyroid-Stimulating Hormone) →TSH is the pituitary hormone that tells your thyroid how hard to work — it is the primary screening test for thyroid function.
- Vitamin B12 →Vitamin B12 is essential for nerve function and red-blood-cell formation — a deficiency can cause anemia and neurological symptoms.
- Ferritin →Ferritin is the protein that stores iron in your body — it is the single best blood marker of how much iron you have in reserve.
- All lab markers →Browse every biomarker guide in one place.
This page provides educational health information and does not replace professional medical advice, diagnosis, or treatment. Interpret any lab value with your clinician, who has your full medical context. For emergencies, contact emergency services.