Markers · Thyroid
TPO antibodies flagged high, with a TSH that's still normal. TPO antibodies, read against the rest of you.
What TPO antibodies measure, what they do in the body, why they're tested, and the two ranges they're read against. Everything said about the marker here comes from Merlin's own biomarker catalogue.
What TPO antibodies are
Thyroid peroxidase antibodies are autoantibodies produced by the immune system that mistakenly target thyroid peroxidase, an enzyme essential for thyroid hormone synthesis. Elevated TPO antibodies indicate autoimmune activity against the thyroid gland, most commonly associated with Hashimoto's thyroiditis or Graves' disease. Persistently high levels suggest ongoing immune-mediated thyroid damage that can progressively impair thyroid function and lead to hypothyroidism over time.
What they do in the body
Thyroid peroxidase is a key enzyme located on the apical surface of thyroid follicular cells that catalyzes the oxidation of iodide and the incorporation of iodine into thyroglobulin, facilitating the synthesis of thyroxine (T4) and triiodothyronine (T3). When the immune system generates antibodies against TPO, this enzyme's function is disrupted and complement-mediated cytotoxicity destroys follicular cells, progressively reducing the thyroid gland's capacity to produce adequate thyroid hormones.
Why they're tested
TPO antibody testing is used to diagnose and confirm autoimmune thyroid conditions including Hashimoto's thyroiditis and Graves' disease, to evaluate the cause of hypothyroidism or hyperthyroidism, to assess risk of thyroid dysfunction in individuals with other autoimmune diseases, and to monitor disease activity. It is also used in pregnancy to identify women at risk for postpartum thyroiditis and neonatal thyroid dysfunction.
The two ranges
The reference range reflects population statistics. The target reflects physiology.
- Lab reference range
- < 35 IU/mL (most laboratory reference ranges; some labs use < 34 or < 60 IU/mL depending on assay methodology)
- Functional target
- 0-6.8 IU/mL
Those are different numbers, and you deserve to know which one you're looking at. Merlin reads your result against both.
Where this lives
A Field Guide to Thyroid & Adrenal Health
The field guide that covers TPO antibodies in depth, whole and public.
In a real read
The real read on this site is a Cardiovascular one, so there's no thyroid panel in it. What it shows is the shape: one system, thought all the way through, with the score, the narrative and the layers underneath. A thyroid panel gets one of these too, with the antibodies read beside the hormones they can affect.
A real Cardiovascular surface from a real anonymized panel: the score, the narrative, the layers underneath. Yours will be built the same way, on your own numbers.
Educational context for your conversations with your licensed healthcare provider, not a diagnosis or a treatment plan. Merlin reads results; it doesn't diagnose.
Read next to
No TPO antibody result yet? You can order it inside Merlin: it's on Thyroid Complete ($99).
Bring the panel this number came from. Merlin reads it against everything else you have, every system and every year, then shows you what it means and what's worth finding out next. Start with your first month.