TPO Antibodies
Also written as: Thyroid peroxidase antibodies, Anti-TPO, TPOAb
Antibodies against a thyroid enzyme, used as a marker of autoimmune thyroid conditions.
What it measures
The level of antibodies directed against thyroid peroxidase, an enzyme the thyroid uses to make its hormones. These antibodies are a marker that the immune system is reacting against the thyroid gland.
Why a doctor orders it
Ordered when thyroid hormone tests are abnormal or borderline, to see whether an autoimmune process such as Hashimoto's thyroiditis or Graves' disease may be behind it. It is sometimes checked as part of pregnancy planning or recurrent miscarriage assessments.
What is generally associated with a higher result
Broadly associated with autoimmune thyroid conditions, including Hashimoto's thyroiditis and Graves' disease. Notably, a fair proportion of healthy people carry these antibodies without ever developing thyroid disease, so their presence alone does not mean the gland is failing.
What is generally associated with a lower result
Low or undetectable levels are the usual finding and are generally not pursued.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- A minority of healthy people, especially women and older adults, test positive without any thyroid problem
- Other autoimmune conditions in the person or their family
- Pregnancy and the year after childbirth, when thyroid antibody levels can shift
- Laboratory method - different labs use different assays and units
Questions to take to your appointment
- What does it usually mean when these antibodies are present while thyroid hormone levels are normal?
- Is there any value in re-checking antibody levels over time?
- Does this result matter for a current or planned pregnancy?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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