What is Protein C?


Normally, blood is maintained in a fluid state in the body as a result of a delicate balance between proteins that make clots (also called coagulants or factors) and proteins that prevent clotting (also called anticoagulants). Most of these proteins are in balance with each other maintaining the fluid state of blood.

            Blood clotting occurs when there is damage to the blood vessel wall. Platelets, tiny blood cells, which are like sticky jigsaw puzzle pieces plug the bleeding point and at the same time, release chemicals that start the clotting process. In addition, tissue fluids (also called tissue factor) released as a result of injury, cause activation of clotting factors. The outcome is like a domino effect that eventually leads to formation of a clot (also called a thrombus). Whenever a blood clot is formed, anticoagulants are also activated and prevent excess clot formation.

Clots can occur in veins (venous) or arteries (arterial).  Arteries are tougher, elasticized blood vessels that carry blood away from the heart and deliver oxygen to the body.  Thrombosis in an artery may cause stroke, heart attack, or damage to limbs or other organs depending on the area of the arterial circulation affected.  Other common contributing causes of arterial thrombosis are cigarette smoking, high blood pressure, high cholesterol, and diabetes.

Veins are thinner, collapsible blood vessels that carry blood back from the tissues to the heart.  It is estimated that 500,000 Americans will incur a blood clot in the large veins in the body (deep vein thrombosis).  These blood clots are often associated with surgery, pregnancy, birth control pills, or other external factors.

Protein C is an anticoagulant, blood thinner, and requires vitamin K for its production. The function of Protein C is to inactivate two activated clotting proteins named factor V and factor VIII.  If there is a deficiency of Protein C, these clotting proteins remain activated so there is more of a tendency for blood to clot. Such a deficiency can be inherited or acquired (vitamin K deficiency, medications, infections, etc.).


What is Congenital Protein C Deficiency?


  • Congenital Protein C deficiency is a potential risk factor for forming venous clots. 


  • Protein C deficiency is rare and is present in about 0.2% of the general population.


  • Only one out of every 1000 persons with congenital protein C deficiency will incur a blood clot in the large veins in the body (deep vein thrombosis).


  • Protein C Deficiency is an inherited disorder.  If one inherits an abnormal protein C gene from only one parent, it is called heterozygous protein C deficiency. Such individuals may be at an increased risk of developing blood clots before 40-45 years of age.


  • If one inherits abnormal protein C genes from both parents, it is called homozygous protein C deficiency.  This is a life threatening condition. It is also called purpura fulminans and can present in the newborn period with extensive blood clots in the brain, vital organs and extremities. Fortunately this is very rare.


Treatment for Protein C Deficiency


  • Treatment of homozygous protein C deficiency requires immediate replenishment of protein C in the blood. This is accomplished by transfusing fresh frozen plasma or the more recently available protein C concentrates.


  • Homozygous and heterozygous individuals with protein C deficiency who develop blood clots are treated with anticoagulants or blood thinners.


  • Anticoagulants or blood thinners are medications and include heparin, low molecular weight heparin (LMWH), and coumadin.   They are generally given for a period of 3-6 months.


  • In some individuals with multiple episodes of blood clots, these medications may have to be taken for a longer period of time.


  • Anticoagulants do have undesirable side effects such as bleeding or further clot formation and need careful supervision.




  1. Avoid long periods of bed rest.  Avoid prolonged sitting or standing in one position.
  2. Do not smoke.
  3. Exercise regularly.
  4. Use support stockings if you have severe varicose veins.
  5. Avoid knee socks or hosiery that might limit blood flow.
  6. Don’t cross ankles or legs while setting or lying.
  7. Keep your feet higher than your hips while sitting.
  8. Do not take birth control pills.
  9. While resting, occasionally move your legs, ankles and toes to promote circulation.
  10. Tell the doctor or surgeon prior to having surgery about your Protein C Deficiency.
  11. Have other members of your family tested for possible Protein C Deficiency.
  12. If anticoagulation is to be considered, a hematologist (blood doctor) should manage the case.