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Alternative names
A-Th3; AT IIIDefinition Return to top
This 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 Return to top
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.
For an infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test Return to top
The 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.How the test will feel Return to top
When 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 performed Return to top
This 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 Values Return to top
The normal range is 0.20-0.45 mg/ml (milligrams per milliliter).What abnormal results mean Return to top
Lower-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 Return to top
Special considerations Return to top
Birth control pills can cause a slight decrease in AT III levels.
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Page last updated: 28 October 2004 |