Different labs use slightly different normal ranges. But in general, 80% to 120% is considered normal for adults.

What is a normal antithrombin 3 level?

Normal findings Antithrombin activity : Newborn: 35-40% Older than 6 months to adult: 80-130%

What does low antithrombin III mean?

The abnormal gene leads to a low level of the antithrombin III protein. This low level of antithrombin III can cause abnormal blood clots (thrombi) that can block blood flow and damage organs. People with this condition will often have a blood clot at a young age.