Antithrombin; AT III; AT 3; Functional antithrombin III; Clotting disorder - AT III; DVT - AT III; Deep vein thrombosis - AT III DefinitionAntithrombin III (AT III) is a protein that helps control blood clotting. A blood test can determine the amount of AT III present in your body. How the Test is PerformedHow to Prepare for the TestCertain medicines may affect the results of the test. Your health care provider may tell you to stop taking certain medicines or reduce their dose before the test. Do not stop taking any medicine before speaking with your provider. How the Test will FeelWhen the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away. Why the Test is PerformedYour provider may order this test if you have repeated blood clots or if blood thinning medicine does not work. Normal ResultsNormal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results. What Abnormal Results MeanLower-than-normal AT III may mean you have an increased risk for blood clotting. This can occur when there is not enough AT III in your blood, or when there is enough AT III in your blood, but the AT III does not function properly and is less active. Abnormal results may not appear until you are an adult. Examples of complications associated with increased blood clotting are:
Lower than normal AT III may be due to:
Higher than normal AT III may be due to:
RisksThere is little risk involved with having your blood taken. Veins and arteries vary in size from one person 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. Other risks may include:
ReferencesAnderson JA, Kogg KE, Weitz JI. Hypercoagulation states. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 140. Chernecky CC, Berger BJ. Antithrombin III (AT-III) test - diagnostic. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:156-157. Sarode R, Kessler CM. Coagulation and fibrinolysis. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 40. | |
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Review Date: 4/29/2022 Reviewed By: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. No warranty of any kind, either expressed or implied, is made as to the accuracy, reliability, timeliness, or correctness of any translations made by a third-party service of the information provided herein into any other language. © 1997- A.D.A.M., a business unit of Ebix, Inc. Any duplication or distribution of the information contained herein is strictly prohibited. | |
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