TPO Antibodies: A Guide

What Are TPO Antibodies

TPO antibodies (anti-TPO) are autoantibodies directed against thyroid peroxidase — an enzyme essential for the production of thyroid hormones. When the immune system mistakenly attacks this enzyme, thyroid function can be disrupted.

The TPO antibody test is one of the most important markers for evaluating autoimmune thyroid disease. Elevated levels can be detected months or even decades before thyroid function actually becomes impaired.

Reference Ranges

TPO antibody levels should be less than 9 IU/mL (or kIU/L). Some laboratories use different cut-offs (e.g., <34 IU/mL) — the limit specified by your laboratory takes priority.

It is important to understand that small amounts of TPO antibodies can be detected in the blood of entirely healthy individuals, particularly in women and older adults.

Why TPO Antibodies May Be Elevated

Elevated TPO antibody levels are most commonly associated with:

• Hashimoto's thyroiditis: the most common autoimmune thyroid disease and the most common cause of hypothyroidism. Over time, the thyroid may lose its ability to produce sufficient hormones
• Graves' disease: autoimmune hyperthyroidism. Although the primary marker is TRAb antibodies, TPO antibodies are also frequently elevated
• Postpartum thyroiditis: a temporary thyroid dysfunction that can appear after childbirth
• Other autoimmune conditions: type 1 diabetes, coeliac disease, rheumatoid arthritis — these conditions are more frequently found alongside elevated TPO antibodies
• Iodine excess: very high doses of iodine can trigger an autoimmune response

Why TPO Antibodies May Be Undetectable

A negative TPO antibody result (below the threshold) is generally good news — it means autoimmune thyroid disease is unlikely. However, a small proportion of patients with Hashimoto's thyroiditis may have negative TPO antibodies; in such cases, anti-TG (thyroglobulin) antibodies are tested.

What to Do Next

1. If TPO antibodies are elevated but TSH is normal — monitor TSH every 6–12 months 2. If elevated and TSH is also abnormal — discuss treatment options with your doctor 3. Check FT4 and FT3 alongside TSH for a complete thyroid profile 4. Consider an anti-TG antibody test — especially if TPO is negative but symptoms are present 5. Ensure adequate selenium, zinc, and vitamin D levels — research suggests potential benefit for thyroid health

Monitoring Over Time

TPO antibody levels can fluctuate — sometimes decreasing, sometimes increasing. Retesting every 6–12 months is worthwhile, especially if levels were previously elevated. The most important monitoring marker is TSH — even with antibodies present, thyroid function may remain normal for a long time.

Tracking the trend on the QbiLabs platform helps you understand whether the situation is changing.

Questions for Your Doctor

• Do my elevated TPO antibodies mean I have Hashimoto's thyroiditis?
• How often should I have my thyroid function checked?
• Should I test for other autoimmune markers (anti-TG, ANA)?
• Can diet and supplements help reduce antibody levels?
• What is the likelihood that my thyroid function will deteriorate in the future?

*This is not medical advice. Consult your doctor regarding any health decisions.*