Skip navigation
MedlinePlus Trusted Health Information for You U.S. National Library of MedicineNational Institutes of Health
Contact Us FAQs Site Map About MedlinePlus
español Home Health Topics Drug Information Medical Encyclopedia Dictionary News Directories Other Resources

 

Medical Encyclopedia

Other encyclopedia topics:  A-Ag  Ah-Ap  Aq-Az  B-Bk  Bl-Bz  C-Cg  Ch-Co  Cp-Cz  D-Di  Dj-Dz  E-Ep  Eq-Ez  F  G  H-Hf  Hg-Hz  I-In  Io-Iz  J  K  L-Ln  Lo-Lz  M-Mf  Mg-Mz  N  O  P-Pl  Pm-Pz  Q  R  S-Sh  Si-Sp  Sq-Sz  T-Tn  To-Tz  U  V  W  X  Y  Z  0-9 

Antithrombin III

Printer-friendly versionEmail this page to a friend
Contents of this page:

Alternative names   

A-Th3; AT III

Definition    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.

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 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: Other conditions that can be related to lower-than-normal AT III include: Higher-than-normal AT III may indicate:

What the risks are    Return to top

Special considerations    Return to top

Birth 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: 6/1/2003

Updated by: Marcia S. Brose, M.D., Ph.D., Division of Hematology/Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

adam.com logo

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 2002 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.