Report of the working party on homozy-gous protein C deficiency of the Subcommittee on Protein C and Protein S, International Committee on Thrombosis and Haemostasis. Protein C deficiency is caused by mutations in the PROC gene. This gene provides instructions for making protein C, which is found in the bloodstream and is important for controlling blood clotting. Protein C blocks the activity of (inactivates) certain proteins that promote blood clotting. Protein C is a vitamin K-dependent zymogen that has essential roles in the regulation of thrombosis and hemostasis. Physiologic activation of protein C occurs at the surface of endothelial cells, with acceleration by thrombomodulin. Protein C is a natural anticoagulant. This is part of the body’s safety. Protein C deficiency is associated with an increase in the risk of venous thrombosis (clots in the veins), especially in the legs. There is also a lesser association with arterial clots at a young age. Most protein C deficiency is inherited, or passed down from one or both parents. It can also be acquired in patients with liver or kidney disease, in patients with HIV, or if you have a vitamin K deficiency. To assist practitioners in managing patients with a suspected or confirmed deficiency in protein C, protein S and antithrombin and to facilitate appropriate referrals to a coagulation specialist. CEPROTIN is for those patients who either don’t produce enough Protein C or whose Protein C doesn’t work correctly. CEPROTIN allows your body’s blood clotting process to function properly.