Any of 13 factors in the blood, including fibrinogen and prothrombin, the actions of which are essential for blood coagulation. Also known as clotting factor.
A group of substances present in blood plasma that, under certain circumstances, undergo a series of chemical reactions leading to the conversion of blood from a liquid to a solid state. Although they have specific names, most coagulation factors are referred to by an agreed set of Roman numerals. Lack of any of these factors in the blood results in the inability of the blood to clot.