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Protein C is a substance 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. For information on how this is done, see: Venipuncture
Certain drugs can interfere with this test. Be sure to tell your doctor about all medications and supplements you are taking before having this test.
Some medicines that prevent blood clots from forming (anticoagulants), such as warfarin (Coumadin), decrease protein C and protein S levels. Your doctor may ask you to stop taking these medications for a time before the test.
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Your doctor may order this test if you have an unexplained blood clot, or a family history of blood clots. Protein C and protein S help regulate blood clotting. A lack of these proteins may cause blood clots to form in veins.
The test is also used to screen relatives of patients with a known protein C deficiency. It may also be done to find the reason for repeated miscarriages.
Bauer KB. Hypercoagulable states. In: Hoffman R, Benz EJ Jr., Shattil SJ, et al, eds. Hoffman Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingstone Elsevier; 2008:chap 134.
Schafer A. Thrombotic disorders: Hypercoagulable states. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 182.
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