TPO antibodies: what a positive result means
A positive thyroid peroxidase (TPO) antibody test is the hallmark of Hashimoto's thyroiditis. It is also common, often found in people who feel well, and frequently misunderstood. Here is what the result does and does not tell you.
Key takeaways
- TPO antibodies show that the immune system is targeting the thyroid; they do not by themselves mean the thyroid is failing.
- About 1 in 8 adults has positive TPO antibodies, more often women and older adults.
- With a normal TSH, the yearly chance of developing hypothyroidism is small, roughly 2 to 4 percent, and higher when TSH is already mildly elevated.
- Antibody levels do not guide treatment. TSH and free T4 do.
- In pregnancy, positive TPO antibodies matter, and TSH should be checked early and often.
What TPO antibodies are
Thyroid peroxidase is an enzyme the thyroid uses to make thyroid hormone. In Hashimoto's thyroiditis, the immune system produces antibodies against it. A blood test for these antibodies is the most sensitive marker of autoimmune thyroid disease: they are present in roughly 90 percent of people with Hashimoto's. Thyroglobulin antibodies (TgAb) are a second, less sensitive marker.
Positive antibodies with a normal TSH
This is the most common situation. It means autoimmune thyroiditis is present, but the thyroid is still making enough hormone. Many people stay in this stage for years or for life. Treatment with levothyroxine is not needed when TSH and free T4 are normal. A sensible plan is to check TSH about once a year, sooner if symptoms appear, and before or early in pregnancy.
Over time, some people progress. In long-term population studies, the risk of developing an underactive thyroid was about 2 percent per year in women with positive antibodies and a normal TSH, and about 4 percent per year when TSH was already mildly raised. The spectrum from antibodies to hypothyroidism.
Do the antibody numbers matter?
Not much for day-to-day decisions. A very high level suggests a somewhat greater chance of eventually needing treatment, but antibody levels fluctuate, differ between laboratories, and do not track symptoms. Repeating the antibody test does not change management, so once it is positive, follow TSH and free T4 instead.
Can antibodies cause symptoms on their own?
This is an area of active debate. Some studies link positive antibodies with fatigue or lower quality of life even when thyroid hormone levels are normal, but this has not been shown to improve with levothyroxine. When symptoms persist with normal labs, it is worth looking for other causes as well. Symptoms with normal labs.
Pregnancy and fertility
Positive TPO antibodies are associated with a higher risk of miscarriage and preterm delivery, and the thyroid may not keep up with the increased demand of pregnancy. Women with positive antibodies should have TSH checked before conception if possible, as soon as pregnancy is confirmed, and about every four weeks during the first half of pregnancy. Treatment is started if TSH rises above the pregnancy target, and may be considered at lower thresholds in some situations. Hashimoto's, pregnancy and fertility.
Can antibodies be lowered?
Selenium supplements modestly lower antibody levels in some studies, but there is no consistent evidence that this protects thyroid function or improves how people feel, and excess selenium has risks. Gluten-free diets lower antibodies only in people who have celiac disease. We do not recommend treating the antibody number itself. Nutrition and Hashimoto's.
When to see an endocrinologist
See an endocrinologist if TSH is abnormal, if you are pregnant or planning pregnancy, if you have a goiter or a nodule, or if you feel unwell and want a careful review. In San Diego, our physicians see patients at Diabetes & Endocrine Specialists.
Sources: Hollowell JG, et al. Serum TSH, T4, and thyroid antibodies in the United States population (NHANES III). J Clin Endocrinol Metab. 2002;87:489–499. Vanderpump MP, et al. The incidence of thyroid disorders in the community: a twenty-year follow-up of the Whickham Survey. Clin Endocrinol. 1995;43:55–68. Alexander EK, et al. 2017 ATA Guidelines for Thyroid Disease During Pregnancy and the Postpartum. Thyroid. 2017;27:315–389. Reviewed October 2026.
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