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 (see blood coagulation). Although they have specific names, most coagulation factors are referred to by an agreed set of Roman numerals (e.g. Factor VIII, Factor IX). Lack of any of these factors in the blood results in the inability of the blood to clot. See also haemophilia.
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substances in the blood that are essential to the clotting process and hence, to the maintenance of normal hemostasis. They are designated by Roman numerals, to which the notation “a†is added to indicate the activated state. Platelet factors (q.v.) also play a role in coagulation.Medical dictionary. 2011.