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Protein C
Definition:
A blood test that measures the amount of protein C.

How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (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 tourniquet 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.

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:

Adults:
Certain medications can interfere with this test. Your doctor may ask you to discontinue these medications for a time prior to the test. Be sure to tell you doctor all medications and supplements which you are taking prior to taking this test.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test will feel:
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:
Protein C and protein S are involved in regulation of coagulation (blood clotting); they inactivate factors V and VIII. Deficiencies may lead to the formation of blood clots in arteries or veins.
Normal Values:
Normal values are 60% to 150% inhibition.
What abnormal results mean:

Deficient protein C can result in excessive clotting. These clots tend to form in veins, not arteries.

Protein C deficiency can be either inherited or acquired in association with other conditions. Liver disease, disseminated intravascular coagulation (DIC), warfarin, and chemotherapy can result in decreased protein C levels
What the risks are:
  • excessive bleeding
  • fainting or feeling light-headed
  • hematoma (blood accumulating under the skin)
  • infection (a slight risk any time the skin is broken)
  • multiple punctures to locate veins
Special considerations:
Protein C and Protein S are decreased by Vitamin K antagonist oral anticoagulants (such as Coumadin, warfarin). Measurements of Protein C or S may be difficult to interpret in patients on oral anticoagulants. During an acute thrombotic episode, Proteins C and S are reduced even if decreased C or S is not the cause of the thrombosis, and measurements of Protein C or S may be misleading until the acute episode is resolved.

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.
Review Date: 10/28/2001
Reviewed By: Rebecca Elstrom, M.D., Division of Hematology-Oncology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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