The liver makes most of the body’s protein C and plays an important role in turning inactive protein C into its active form. In certain cases, protein C deficiency can occur as the result of health problems, such as vitamin K deficiency. Use of blood thinners such as warfarin (Coumadin, Jantoven) and heparin can interfere with your body’s ability to activate protein C. This can also be owing to widespread metastatic tumors or severe illness, including infection (sepsis). Protein C may be used up rapidly by the body in these situations or destroyed by bacteria or other microorganisms during infection.