Lab test glossary · Thyroid
Thyroid Antibodies (TPO): what it means
Also known as: thyroid peroxidase antibodies, anti-TPO, TPOAb
TPO antibodies are immune proteins aimed at the thyroid; a positive result points to autoimmune thyroid disease such as Hashimoto's.
What it measures
Thyroid peroxidase (TPO) antibodies are made when the immune system targets an enzyme the thyroid uses to make hormone. Their presence is the hallmark of autoimmune thyroid conditions — most often Hashimoto's thyroiditis (which tends toward an underactive thyroid) and sometimes Graves' disease. They help explain why a thyroid is misbehaving.
Typical range
Reported as positive or negative against a lab cutoff; a low-level positive can occur in people without thyroid disease, so results are read with TSH and symptoms.
Reference ranges differ between labs and are printed on your own report — always read your result against that range, not a general one.
What a high result can mean
- Autoimmune thyroid disease (Hashimoto's, Graves')
- Can be mildly positive in some people without thyroid problems
A high value is a starting point for a conversation, not a diagnosis — many causes are benign or temporary.
Why the trend matters
Antibody levels can change over time, but the key question is usually presence plus how the thyroid itself (TSH, free T4) is behaving.
When to talk to your doctor
Discuss positive TPO antibodies with your doctor, particularly alongside an abnormal TSH or thyroid symptoms.
This page is general education about a common lab test — it isn’t medical advice and can’t interpret your specific result. What a value means depends on your history, symptoms, and the rest of your labs, which is a conversation for you and your clinician.