TPO Antibodies
Autoantibodies against thyroid peroxidase – primary marker for autoimmune thyroiditis
Also known as
Definition
TPO antibodies (anti-TPO, microsomal antibodies) are autoantibodies against thyroid peroxidase, a key enzyme in thyroid hormone synthesis. They are elevated in more than 90% of Hashimoto's thyroiditis cases and in ~70% of Graves' disease. Elevated TPO antibodies without clinical symptoms or TSH change are termed latent autoimmune thyroiditis. They are a predictor of future hypothyroidism development.
| Parameter | Value |
|---|---|
| Unit | IU/ml (U/ml) |
| Reference Range | < 35 IU/ml (lab-dependent; some labs: < 60 IU/ml) |
Agree on your personal target range with your doctor.
↓ What a low value means
Low or negative TPO antibodies (< 35 IU/ml) argue against active autoimmune thyroiditis. No pathological condition is known at very low values. A negative result does not fully exclude autoimmune thyroiditis (5–10% of Hashimoto's cases are seronegative).
↑ What a high value means
Elevated TPO antibodies (> 35 IU/ml) indicate autoimmune thyroiditis. Antibody titer levels do not always correlate with disease severity. Together with TSH, fT3, and fT4, they determine whether hypo- or hyperthyroidism is already present. Elevated values increase the risk of future thyroid dysfunction, postpartum thyroiditis, and miscarriage.
✓ What can influence this value
The TPO antibody titer is determined mainly by the underlying autoimmune thyroid disease (Hashimoto's thyroiditis, Graves' disease); the level of the titer does not always correlate with the severity of the disease. Selenium, vitamin D, inositol, stress, alcohol and tobacco consumption, and gluten with coexisting celiac disease have been studied as possible influencing factors. Reference ranges depend on the laboratory, and results from different laboratories are only partly comparable. The assessment is made by the treating doctor.
When to test
With thyroid dysfunction (TSH change), suspected Hashimoto's or Graves' disease, infertility, recurrent miscarriages, postpartum depression, autoimmune disease, or family history of thyroid disease. How often a positive initial finding is followed up is decided by your doctor.
Frequently asked questions
Can I live with elevated TPO antibodies and no symptoms? +
Yes, many people have elevated TPO antibodies without symptoms or with normal thyroid function (euthyroid autoimmune thyroiditis). In the Whickham cohort, followed for 20 years, the risk of later hypothyroidism was higher with positive thyroid antibodies; how much higher depended on the TSH level and sex, among other things. A general lifetime rate cannot be derived from this. How often values are checked and whether treatment is given is decided by your doctor.
Hashimoto's or Graves' — how do the antibodies differ? +
TPO antibodies (anti-TPO) are elevated in both conditions. More specific to Graves' disease are TRAb (TSH receptor antibodies / anti-TSHR), which stimulate the thyroid to overproduce. Anti-thyroglobulin (TgAb) can occur in both. The combination of TSH + fT3 + fT4 + anti-TPO + TRAb enables differentiation.
What role does gluten play in Hashimoto's? +
Only with coexisting celiac disease or confirmed non-celiac gluten sensitivity is there evidence of benefit (antibody normalization with a gluten-free diet). In Hashimoto's without celiac disease, the evidence for gluten-free eating is weak.
Does selenium really affect TPO antibodies? +
Multiple randomized controlled trials (including meta-analyses) show that selenomethionine significantly lowers TPO antibody titers in Hashimoto's (~20–30%). Whether and how treatment is given is decided by your doctor.
TPO Antibodies
Sources
- Stassi G, De Maria R (2002) Autoimmune thyroid disease: new models of cell death in autoimmunity. Nat Rev Immunol.
- Toulis KA et al. (2010) Selenium supplementation in the treatment of Hashimoto's thyroiditis: a systematic review and meta-analysis. Thyroid.
- Kahaly GJ et al. (2017) European Thyroid Association Guideline for the Management of Graves' Hyperthyroidism. Eur Thyroid J.
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.