Factor Xa Inhibitor (Antithrombin Activity)

What Does This Test Measure?

Antithrombin is a protein produced by your liver that acts as a natural anticoagulant. It binds to and inactivates Factor Xa, a protein involved in the clotting cascade. This test evaluates the functional activity of antithrombin by measuring its ability to inhibit Factor Xa in your blood. This is often done in patients suspected of having antithrombin deficiency or those on anticoagulant therapy to monitor effectiveness.

Why Might This Test Be Ordered?

Your healthcare provider may order this test if you have a history of blood clots, bleeding disorders, or if you’re taking anticoagulant medications like heparin or warfarin. It may also be used to diagnose or monitor conditions like antithrombin deficiency, which can increase your risk of clotting problems.

How Is the Test Performed?

A blood sample is drawn from a vein, usually in your arm. The sample is processed to measure antithrombin’s ability to inhibit Factor Xa. The test may use a method like chromogenic assay, which detects clotting activity indirectly by measuring enzyme activity.

What Are Possible Results?

Results are typically reported as a percentage or ratio of normal antithrombin activity. A result below the normal range may indicate a deficiency in antithrombin, which could increase your risk of clotting. Your provider will interpret results in the context of your medical history and symptoms.