Serum or Plasma Antithrombin III Concentration (Mass Concentration)

Why This Test Might Be Ordered: Your healthcare provider may order this test to help diagnose a medical condition, check how well a treatment is working, or screen for potential problems before symptoms appear. It is often included in a routine exam or used to investigate symptoms such as fatigue, weakness, or unexplained changes in your health.

Your healthcare provider may order this test if you have a history of blood clots, certain blood disorders, kidney disease, or if you’re taking medications that affect blood clotting. It may also be done before surgery or during treatment for conditions like disseminated intravascular coagulation (DIC).

What to Expect Before the Test: Before the test, your care team will give you specific instructions. You may need to fast for a certain number of hours, avoid certain foods, drinks, or medications, or schedule the test at a particular time of day. Tell your provider about all medicines, vitamins, and supplements you take, and mention any allergies or bleeding problems.

No special preparation is usually needed. You may have a small needle inserted into your arm to draw blood. If you’re on blood-thinning medication, check with your provider first, as it may affect results.

What the Test Results Mean: Your results are compared with a normal reference range, and your provider will interpret them based on your age, sex, medical history, and current medications. A result that is higher or lower than expected does not always mean you have a serious condition, but it helps your care team decide whether further testing or treatment is needed.

Results are compared to a standard range for healthy adults. Low levels may indicate increased risk of clotting, while very low levels could signal underlying conditions like liver disease or certain cancers.

Common Conditions Monitored: This test is commonly used to monitor conditions such as diabetes, thyroid disorders, anemia, kidney disease, and liver disease. It may also be checked regularly in people taking medications that can affect these organs, so changes can be detected early and treatment plans adjusted when needed.

Antithrombin III is often checked in people with inherited or acquired clotting disorders, those receiving anticoagulant therapy, or those with conditions like thrombophilia or liver disease.