A factor VIII activity blood test lets doctors evaluate the functioning of a protein that helps blood to clot. A clot is a lump of blood that the body produces to prevent excessive bleeding by sealing leaks from blood vessels caused by wounds, cuts, scratches, or other conditions.
In this manner, where does factor VIII come from?
Factor VIII is produced in liver sinusoidal cells and endothelial cells outside the liver throughout the body. This protein circulates in the bloodstream in an inactive form, bound to another molecule called von Willebrand factor, until an injury that damages blood vessels occurs.
Is Factor VIII an enzyme?
Among the known clotting factors, factors VIII and V are exceptional in not possessing enzymatic activity. Factor VIII is inactivated by thrombin and by activated protein C. Thus, factor VIII can be modulated by at least four of the serine proteases in the clotting system.
What activates Factor V?
Factor V is able to bind to activated platelets and is activated by thrombin. The thereby activated factor V (now called FVa) is a cofactor of the prothrombinase complex: The activated factor X (FXa) enzyme requires calcium and activated factor V to convert prothrombin to thrombin on the cell surface membrane.