Test Details: Proteins S acts as a principal cofactor to protein C. The two work together to help regulate and control blood clot formation by inactivating specific coagulation factors (factors V and VIII) that are required to generate and form blood clots. This has the net effect of slowing down clot formation. Therefore, if there is not enough protein C or S or they are not functioning normally, clot formation can go unchecked, possibly leading to excessive clotting. These conditions can range from mild to severe.