Antithrombin III Activity (Serum or Plasma)

Why Is This Test Done?

Your doctor may order this test if you have a history of blood clots, bleeding problems, or certain medical conditions that affect blood clotting, such as liver disease or inherited clotting disorders. It may also be used to monitor treatment for conditions like disseminated intravascular coagulation (DIC) or to check for deficiencies that could increase your risk of clotting.

What to Expect Before the Test

You may be asked to fast for a few hours before the test, but this isn’t always required. Bring any medications you’re taking to your appointment. Avoid smoking and consuming alcohol for at least 24 hours before testing, as they can affect blood clotting.

A healthcare provider will draw blood from a vein in your arm using a needle. The blood sample will be sent to a lab for analysis, where it will be tested for antithrombin III activity.

The blood sample is typically processed within a few hours. Results are usually available within 24 to 48 hours, depending on lab procedures and urgency.

Low levels of antithrombin III may indicate an increased risk of blood clots, while very high levels might suggest liver disease or other conditions affecting protein production. Your doctor will interpret the results in the context of your medical history and symptoms.

Normal results vary by lab and may not apply to everyone. Your doctor will discuss the meaning of your specific results with you.