TPO Antibodies Explained: Normal Range & What Positive Means
Also known as: Anti-TPO, TPOAb, thyroid peroxidase antibody, antithyroid antibodies
Thyroid peroxidase (TPO) antibodies are immune proteins that mistakenly target an enzyme your thyroid uses to make hormone. Measuring them helps identify autoimmune thyroid disease such as Hashimoto's thyroiditis and Graves' disease. A normal TPO antibody level is typically below about 9–35 IU/mL depending on the lab; a positive (elevated) result signals thyroid autoimmunity but does not, by itself, mean you have thyroid dysfunction.
TPO Antibodies normal range
| Category | Range (IU/mL) |
|---|---|
| Negative / normal | < 9–35 IU/mLCutoff depends on the lab and assay |
| Positive / elevated | ≥ lab cutoffIndicates thyroid autoimmunity |
| Strongly positive | hundreds–thousands IU/mLCommon in Hashimoto's thyroiditis |
| Reference ranges vary by lab | Use your own reportCutoffs differ substantially between labs |
Reference ranges vary by laboratory. Use the range printed on your own report as the definitive comparison.
What high TPO Antibodies can mean
- Hashimoto's thyroiditis (the most common cause of a strongly positive result)
- Graves' disease
- Autoimmune thyroiditis that may not yet affect thyroid function
- A modest number of healthy people carry TPO antibodies without thyroid disease
What low TPO Antibodies can mean
- A negative/low TPO antibody level is the normal, expected result
- It makes autoimmune thyroid disease less likely but doesn't fully exclude it
What to do about an abnormal result
- Compare your value to the cutoff on your own report — TPO antibody thresholds vary widely between labs.
- A positive result is interpreted with TSH and free T4; antibodies alone don't determine whether treatment is needed.
- If you have positive antibodies but normal thyroid function, your doctor may simply monitor your TSH over time.
- Don't self-diagnose from one number — a positive result is common and doesn't always mean current thyroid disease.
Understand your own results
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Frequently asked questions
What does a positive TPO antibody result mean?
A positive TPO antibody result means your immune system is producing antibodies against your thyroid, indicating autoimmune thyroid disease such as Hashimoto's or Graves'. It signals a higher risk of thyroid dysfunction over time, but on its own it doesn't mean your thyroid isn't working normally right now.
What is a normal TPO antibody level?
Normal is usually below the lab's cutoff, often somewhere between 9 and 35 IU/mL, though this varies by assay. Values above the cutoff are considered positive, and levels in the hundreds or thousands are common in Hashimoto's thyroiditis.
Can you have TPO antibodies and a normal thyroid?
Yes. Some people have detectable TPO antibodies with completely normal thyroid function, and a portion never develop thyroid disease. Because antibodies raise future risk, doctors typically monitor TSH periodically rather than treating the antibodies themselves.
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Medically reviewed by Antonieta Rueda, MD and Kyle R. Toth, MD · Last reviewed July 6, 2026
This article is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or your lab results.