Total Antithrombin III Level (Serum or Plasma)

Your healthcare provider may order this test to help find the cause of symptoms you are experiencing, to check how well a current treatment is working, to screen for a health condition before it causes problems, or as part of a routine checkup to monitor your overall health over time.

Your doctor may recommend this test if you have a history of blood clots, certain blood disorders, or conditions that affect protein production in your liver. It may also be used to monitor treatment for conditions like disseminated intravascular coagulation (DIC) or antithrombin deficiency.

Before the test, your provider will give you specific instructions to follow. You may be asked to stop taking certain medicines or supplements, avoid food or drinks for a set period of time, or arrive with a full bladder. Tell your care team about any medicines you take, any allergies you have, and any medical conditions, and plan to arrive a little early so you have time to check in and ask questions.

No special preparation is usually needed. You may be asked to fast for a few hours before the blood draw, but this depends on your doctor’s instructions. Bring any medications you’re taking to your appointment.

During the test, a trained member of your care team will explain each step and answer any questions you have along the way. Depending on the type of test, you may be asked to sit or lie down while a small sample is collected or while equipment is used to gather the information your provider needs. Most tests take only a short time, and you can usually return to your normal activities right afterward.

A healthcare provider will draw blood from a vein in your arm. You may feel a slight pinch, but the process is quick. The blood sample will be sent to a lab for analysis.

Your results will show whether your values fall within the range considered typical for someone of your age and sex. Results within that range may suggest that things are working as expected, while results outside the range do not always mean something is wrong. Your provider will review the results with you, explain what they mean in the context of your health history, and discuss whether any follow-up testing or changes to your care plan are needed.

Results are compared to a general reference range to determine if your levels are too high or too low. Low levels of antithrombin III can increase your risk of clotting problems, while very high levels may indicate other health concerns.