Anti-TPO Antibody Test
The anti-TPO (anti-thyroid peroxidase) antibody test detects antibodies against an enzyme in the thyroid — a marker of autoimmune thyroid disease, most commonly Hashimoto’s thyroiditis.
It does not measure thyroid function directly but explains why dysfunction occurred.
Last medically reviewed: 1 November 2025
What it detects
Anti-TPO antibodies attack thyroid peroxidase, an enzyme needed for hormone production. Their presence indicates autoimmune thyroiditis — the mechanism behind most hypothyroidism in iodine-sufficient regions.
Positive anti-TPO can occur years before thyroid function declines, identifying people at risk.
When it is ordered
Anti-TPO is checked when hypothyroidism is diagnosed (to confirm autoimmune cause), when TSH is mildly elevated with normal T4 (to assess progression risk), in pregnancy planning (positive antibodies increase miscarriage/preterm risk even with normal function), and in family screening.
It is not a routine screening test for everyone.
Interpreting results
Positive anti-TPO confirms autoimmune thyroiditis but does not predict severity or timing of dysfunction. Some people remain euthyroid with positive antibodies for years.
Negative anti-TPO does not exclude thyroid disease — other antibodies (anti-thyroglobulin) or non-autoimmune causes exist.
Frequently asked questions
Does positive anti-TPO mean I will become hypothyroid?
It increases risk but is not deterministic — many people with positive antibodies maintain normal function for years. Monitoring detects progression.
Should I be tested if my TSH is normal?
Not routinely — anti-TPO is considered when TSH is abnormal or in specific contexts like pregnancy planning or family history.
Is anti-TPO the same as anti-thyroglobulin?
No — they are different antibodies. Anti-TPO is more sensitive for Hashimoto’s; both can be positive. Anti-Tg is also used as a tumour marker after thyroid cancer.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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