Factor Inhibitor Activity in Plasma (e.g., Antithrombin Activity)

Why This Test Might Be Ordered

Your healthcare provider may order this test if you have symptoms like easy bruising, excessive bleeding, or unexplained clots. It’s also used to monitor conditions like antithrombin deficiency or to check how well blood-thinning treatments are working. Sometimes, it’s part of a broader evaluation for inherited or acquired clotting disorders.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for a few hours before your blood draw if your provider specifies it. Bring a list of all medications or supplements you take, as some can affect test results. Avoid strenuous activity or eating heavy meals right before the test.

What the Test Involves

A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but it’s typically over quickly. The blood sample is then sent to a lab for analysis. The process usually takes less than 15 minutes.

What the Results Mean

Results are compared to a standard range, but exact values can vary by lab. Low antithrombin activity may indicate a bleeding disorder or an increased risk of clotting, depending on your medical history. High levels might suggest certain liver conditions or medications that boost clotting. Your provider will discuss the results in the context of your overall health.