The human coagulation pathway (blood clotting system) is a complex and delicate balancing act between proteins in the bloodstream that promote clot formation and other proteins in the bloodstream that inhibit clot formation (coagulation factors). In a healthy individual, blood clots form appropriately to stop bleeding. There are a variety of disease states that disrupt the coagulation pathway resulting in the abnormal formation of clots (hypercoagulability) or abnormal excessive bleeding (coagulopathy).
When a blood clot forms and embolizes within the arterial system, it may travel and obstruct the flow of blood to a portion of the brain. The lack of blood flow results in focal brain ischemia, i.e., inadequate blood supply, that can lead to permanent cell death from infarction. This process is referred to as embolic stroke.
Patients with hypercoagulability may be treated with an anticoagulant which is a medication that shifts the balance of the coagulation pathway away from clot formation. Warfarin (Coumadin) has been used to prevent blood clots and the complications thereof since it was approved for use in the United States in 1954. Warfarin is commonly prescribed for patients who suffer from DVT, PE, and arterial emboli such as embolic stroke. Warfarin works by inhibiting the activity of vitamin K which is necessary for the synthesis of certain clotting factors by the liver. By creating a functional vitamin K deficiency, warfarin depletes the supply of coagulation factors that promote clot formation. The result is a drug-induced coagulopathy which is commonly referred to as blood thinning. The degree of blood thinning is measured using the INR blood test. An INR of 1.0 indicates that no warfarin effect is present, while most patients who require blood thinning are maintained at an INR between 2.0 and 3.5. Warfarin is also prescribed to prevent embolic stroke due to atrial fibrillation, a common arrhythmia that promotes clot formation in the heart and subsequent embolization to the brain.
Protein C and protein S are coagulation factors that promote anticoagulation. Therefore, a deficiency of protein C or S results in a hypercoagulable state. Protein C and S levels are commonly tested in patients who suffer from hypercoagulability.