Serum or Plasma Antithrombin III Activity (Qualitative or Quantitative)

Why This Test Is Done

Your doctor may order this test if you have symptoms of bleeding problems, such as easy bruising, excessive bleeding from cuts, or unexplained nosebleeds. It may also be done before surgery to assess your risk of bleeding. Additionally, it could be used to monitor conditions like liver disease, which can affect protein production, or to evaluate patients with inherited clotting disorders.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if your blood is drawn from a vein. If you’re taking blood from a fingerstick, fasting may not be required. Always follow your doctor’s instructions.

How the Test Is Done

A healthcare provider will draw blood from a vein in your arm using a needle. You may feel a small pinch when the needle goes in, but the procedure is quick. The blood sample is then sent to a lab for testing.

What the Results Mean

Results are typically reported as a percentage or ratio compared to a standard. Very low levels may suggest bleeding disorders, liver disease, or other conditions affecting protein production. Very high levels may rarely indicate certain medical conditions or lab errors. Your doctor will interpret the results in the context of your overall health and symptoms.