Hormonology Anti-TPO Thyroid antibodies

Anti-TPO Unit Converter

Convert thyroid peroxidase antibody results between IU/mL, kIU/L, IU/L, U/mL, and kU/L.

Published on: 2026-06-08 · Last updated: 2026-06-08

Enter Anti-TPO value

You can enter a value in any supported unit.
Please enter a valid positive number.

What does this converter do?

This tool converts Anti-TPO values between IU/mL, kIU/L, IU/L, U/mL, and kU/L. It is designed for thyroid peroxidase antibodies, also written as TPOAb, anti-thyroid peroxidase antibody, or microsomal thyroid antibody in some older reports. It converts units only and does not determine whether the antibody result is clinically significant.

Supported units

IU/mL kIU/L IU/L U/mL kU/L

Conversion formulas

IU/mL = kIU/L
kIU/L = IU/mL
IU/L = IU/mL × 1000
IU/mL = IU/L ÷ 1000
U/mL ≈ IU/mL only when the laboratory method defines U as IU
kU/L ≈ kIU/L only when the laboratory method defines kU as kIU

Important notes about Anti-TPO units

Anti-TPO, also called TPOAb or thyroid peroxidase antibodies, is most commonly reported in IU/mL or kIU/L. The numeric value is the same in IU/mL and kIU/L. Some laboratories may report U/mL or kU/L, but these should only be treated as equivalent to IU/mL or kIU/L when the report or assay documentation clearly defines them that way.

  • 1 IU/mL is numerically equal to 1 kIU/L.
  • 1 IU/mL equals 1000 IU/L.
  • U/mL and kU/L may be assay-specific units; do not assume equivalence unless the laboratory method states it.
  • Reference limits for Anti-TPO vary significantly between assay platforms and laboratories.
  • Anti-TPO should be interpreted together with TSH, Free T4, Free T3, Anti-Tg, symptoms, pregnancy status, and the clinical context.

Example conversion

If Anti-TPO = 35 IU/mL, then Anti-TPO = 35 kIU/L and 35,000 IU/L. If the report uses U/mL or kU/L, only convert it as equivalent when the laboratory method confirms that U is used as an international-unit equivalent.

Important laboratory note

Anti-TPO interpretation depends on the assay platform, laboratory cutoff, thyroid function tests, pregnancy status, autoimmune thyroid disease history, symptoms, and clinical context. A positive Anti-TPO result may support autoimmune thyroiditis, but treatment decisions are usually based on the complete thyroid profile and patient assessment, not the antibody value alone.