Heart & coagulation

Antithrombin activity unit converter

Activity of the natural anticoagulant antithrombin (thrombosis risk)

Also known as: Antithrombin III activity, AT III

Converter

Enter a value in any unit and all other units fill in.

IU/mL % = IU/dL

Worked example

104.5 % (middle of the reference range) = 1.04 IU/mL

Conversion formulas

IU/mL	IU/mL = % × 0.01	% = IU/mL × 100

Good to know

Antithrombin activity is reported in % or IU/dL. The page converts between the units only.

1 IU/dL = 1 %; the two notations are interchangeable.
The range shown is a guide from the named source; targets and reference ranges differ between laboratories, methods and indications, so compare with the range on your own report.

Reference range

Unit	Adults
IU/mL	0.88 – 1.21
% = IU/dL	88 – 121

Source: Newcastle Hospitals Laboratories: Antithrombin III · Last reviewed: 2026-10-19

Note from the source: 88-121 IU/dL (= 88-121 %) (Newcastle Hospitals Laboratories)

Frequently asked questions

How do I convert Antithrombin activity from % to IU/mL?

IU/mL = % × 0.01. In the other direction: % = IU/mL × 100.

What is the reference range of Antithrombin activity?

For adults the range is 88 – 121 % (Newcastle Hospitals Laboratories: Antithrombin III). Reference ranges differ between laboratories and partly by sex and age; use the range printed on your lab report.

Which units are used for Antithrombin activity?

Common units are IU/mL, %.