TPO antibodies optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for TPO antibodies:
- Optimal 0 – 9 IU/mL (0 – 9 kIU/L); sufficient 9 – 34 IU/mL (9 – 34 kIU/L); out of range below 0 or above 34 IU/mL.
Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| IU/mL | 0 – 9 | 9 – 34 | below 0 or above 34 |
| kIU/L | 0 – 9 | 9 – 34 | below 0 or above 34 |
What the evidence says
Read this one against the cut-off printed on the report: the two edges here are two manufacturers' positivity cut-offs, not grades of severity. Laboratories on Beckman Coulter assays report positive from 9 IU/mL (Mayo, Worcestershire NHS), Labcorp's adult range runs to 34 IU/mL, and UK laboratories on the newer Roche kit use 20. So a result between 9 and 34 shows here as Sufficient and may be positive on the assay that produced it. A positive result marks thyroid autoimmunity and is the usual antibody finding in Hashimoto's thyroiditis; the number itself is not comparable between laboratories.
Sources
- TPO - Overview: Thyroperoxidase Antibodies, Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceReference value below 9.0 IU/mL at all ages. This is where Sera's optimal band ends, but Mayo treats 9 and above as positive, not as a second acceptable tier.
- Thyroid Peroxidase Abs — Worcestershire Acute Hospitals NHS Trust, 2026 · Laboratory / reference-interval sourceReference range below 9 IU/mL, sourced to Beckman Coulter. Confirms that 9 is the Beckman assay's cut-off.
- Thyroid Peroxidase (TPO) Antibodies — Labcorp, 2026 · Laboratory / reference-interval sourceAdult range of 0 to 34 IU/mL by electrochemiluminescence immunoassay. This is Sera's acceptable upper edge of 34.
- TPO antibody — University Hospitals Sussex NHS Foundation Trust, 2026 · Laboratory / reference-interval sourceReference range below 20 IU/mL from the Roche Cobas Anti-TPO II kit insert, changed on 5 October 2026 with a method change. Shows the Roche cut-off is no longer 34 on the newer kit.
- Thyroid Peroxidase Antibodies — York and Scarborough Teaching Hospitals NHS Foundation Trust, 2026 · Laboratory / reference-interval sourceReference interval below 20 IU/mL, quoted by the manufacturer. A second UK laboratory using 20 rather than 34.
What ATPO (Anti-Thyroid Peroxidase Antibodies) measures
Antibodies that attack thyroid peroxidase, an enzyme the thyroid needs to make its hormones.
Raised ATPO is a sign that the immune system is attacking the thyroid. Tracking it over time helps show whether lifestyle changes are calming that immune attack.