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Alternative namesThis is a blood test that measures the amount of antithrombin III (AT III), a protein that helps prevent and regulate blood clotting.
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
How to prepare for the testThe health care provider may limit certain medications shortly before the test to assure an accurate sample. Usually this will include monitoring drugs that may affect the amount of antithrombin in the bloodstream.
For infants and children:
The preparation you can provide for this procedure depends on your child's age, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics:
How the test will feelWhen the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performedThis test is indicated when there are repeated episodes of blood clots or when individuals do not respond to anticoagulant medications. It can help to determine the cause of hypercoagulation (increased blood coagulation).
Normal ValuesThe normal range is 0.20-0.45 mg/ml (milligrams per milliliter).
What abnormal results meanLower-than-normal AT III may indicate an increased risk of clotting. Examples of disorders and/or conditions associated with increased blood clotting include:
What the risks are
Special considerationsBirth control pills can cause a slight decrease in AT III levels.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Update Date: 6/1/2003Marcia S. Brose, M.D., Ph.D., Division of Hematology/Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT