What does the Antithrombin Activity test measure?

Why is Antithrombin Activity measured?

Antithrombin deficiency — whether hereditary or acquired — increases thrombotic risk and may contribute to recurrent venous thromboembolism, arterial events in young patients, or resistance to heparin during therapeutic anticoagulation. The activity assay measures functional capacity rather than immunoreactive protein, capturing both quantitative and qualitative defects, and is therefore the preferred first-line test when antithrombin deficiency is suspected clinically.

Reference ranges

Standard reference

Approximately 80–120% of normal pooled plasma activity; assay-dependent.

Functional medicine optimal

For most clinical purposes, activity between 80 and 120% is considered normal. Values persistently below 80% warrant investigation for hereditary deficiency or an acquired cause, particularly when associated with recurrent thrombosis or a positive family history.

Units

%, IU/mL

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.