Protein S is a normal substance in your body that prevents blood clotting. A blood test can be done to see how much of this protein you have in your blood.
A blood sample is needed.
Certain medicines can change blood test results:
When 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 slight bruising. This soon goes away.
You may need this test if you have an unexplained blood clot or a family history of blood clots. Protein S helps control blood clotting. A lack of this protein or a problem with the function of this protein may cause blood clots to form in veins.
The test is also used to screen relatives of people who are known to have protein S deficiency.
Sometimes, this test is done to find the cause of repeated miscarriages.
Normal values are 60% to 150% inhibition.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.
A lack (deficiency) of protein S can lead to excess clotting. These clots tend to form in veins, not arteries.
A protein S deficiency may be inherited. It can also develop due to pregnancy or certain diseases, including:
Protein S level rises with age, but this does not cause any health problems.
There 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 associated with having blood drawn are slight, but may include:
Anderson JA, Hogg KE, Weitz JI. Hypercoagulable 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. Protein S, total and free - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:928-930.BACK TO TOP
Review Date: 1/19/2021
Reviewed By: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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