Serum or plasma concentration of antithrombin III (ATIII)

What Is Antithrombin III?

Antithrombin III is a natural protein in your blood that acts as an inhibitor of certain enzymes involved in the clotting process. It helps maintain a balance between blood clotting and bleeding by preventing excessive clot formation. This test helps doctors assess your risk of developing blood clots, especially if you have conditions like blood clotting disorders or are taking certain medications that affect clotting.

Why Might You Need This Test?

Your doctor may order this test if you have a history of blood clots, certain genetic conditions (like antithrombin deficiency), or if you’re taking medications that thin your blood (like warfarin or heparin). It can also be used to monitor treatment progress or check for clotting issues before surgery.

How Is the Test Performed?

A blood sample is drawn from a vein, usually in your arm. The blood is then sent to a lab where it’s analyzed to measure the concentration of antithrombin III. The test can be done on either serum (blood without clotting factors) or plasma (blood with clotting factors).

What Does the Test Result Mean?

Results are typically reported as a percentage or ratio compared to a standard. Very low levels may indicate a higher risk of clots, while very high levels might suggest other health conditions or medications affecting protein levels. Your doctor will interpret the result in the context of your medical history and symptoms.