Finding the right tests…
Emergency services available 24 x 7
Emergency services available 24 x 7
Finding the right tests…
Hormonal
Thyroid peroxidase is an enzyme your thyroid gland uses to build thyroid hormone. TPO antibodies appear when your immune system mistakenly attacks that enzyme, and doctors order this test most often after a thyroid function test comes back abnormal, to see whether an autoimmune condition like Hashimoto's thyroiditis is behind it. Between 90 and 95% of people with Hashimoto's carry these antibodies, which makes the test useful for confirming that diagnosis. That said, a positive result alone doesn't mean you have thyroid disease right now — many healthy people carry TPO antibodies with no thyroid problem, depending partly on dietary iodine. It's also checked during unexplained infertility or recurrent miscarriage, since positive antibodies carry higher pregnancy risk.
This test measures TPO antibody levels in a blood sample using a standard venous draw, with no fasting required. Results are reported in international units per millilitre against a reference cutoff set by the testing lab, and that cutoff varies by assay, so ask your doctor to read your number against their specific reference range rather than a figure found elsewhere. It's usually ordered together with TSH and free T4, since TPO antibodies on their own don't tell your doctor whether your thyroid hormone levels are actually abnormal — that comes from the hormone tests, not the antibody test.
Thyroid peroxidase is an enzyme your thyroid gland uses as a working tool to build thyroid hormone. When thyroid cells are damaged, some of this enzyme leaks into your bloodstream, and in certain people, the immune system reacts to it as if it were foreign, producing TPO antibodies.
Hashimoto's thyroiditis is the most common autoimmune cause of an underactive thyroid, and TPO antibodies show up in the large majority of people who have it, based on research reviewed in the NCBI literature. That's what makes this test genuinely useful once a thyroid hormone test has already come back abnormal — it helps confirm an autoimmune cause rather than another explanation.
Not everyone with TPO antibodies has active thyroid disease. A meaningful share of healthy people, with entirely normal thyroid function, still carry these antibodies, so on its own a positive result is better read as a risk marker than a diagnosis. Doctors weigh it together with TSH, free T4, and your symptoms rather than in isolation.
- Confirms an autoimmune cause once thyroid hormones look abnormal - Doesn't diagnose thyroid disease by itself - Relevant to fertility and pregnancy risk assessment
A positive result usually points to an autoimmune process affecting your thyroid, most often Hashimoto's thyroiditis. Between 90 and 95% of people with Hashimoto's carry these antibodies, according to research reviewed in the NCBI literature, which makes it a useful confirming test.
Yes. Population studies cited in NCBI-reviewed research found TPO antibodies in anywhere from about 13% to 25% of healthy people with no thyroid problem, depending partly on iodine levels in the local diet, so a positive result alone doesn't confirm disease.
Not definitely, but it does raise your future risk. MedlinePlus notes that a positive result doesn't always mean you currently have a thyroid condition or need treatment, though your doctor may want to monitor you over time.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
TPO antibodies are linked to a higher risk of miscarriage, preeclampsia, and premature birth in the research literature, so some doctors check for them during fertility or pregnancy evaluation, particularly alongside thyroid symptoms.
No. Your doctor combines this with your TSH, free T4, symptoms, and sometimes a thyroid ultrasound, since the antibody test alone doesn't measure whether your thyroid hormone levels are actually affected.
No specific fasting requirement is described for this test, but ask your doctor or the centre directly when you book.
A negative result is considered normal, per MedlinePlus, but the exact numeric cutoff used to call a result negative varies between labs and assays. Ranges vary by lab, so check the reference value printed on your own report.