Medical Laboratory Scientist (MLS) ASCP Practice Exam

Factor XII, also known as Hageman factor, plays a pivotal role in secondary hemostasis. This phase follows primary hemostasis, where the initial vascular response and platelet plug formation occur. During secondary hemostasis, the coagulation cascade is activated, leading to the conversion of fibrinogen to fibrin, which solidifies the platelet plug and forms a stable blood clot.

Factor XII initiates the intrinsic pathway of the coagulation cascade by being activated upon contact with negatively charged surfaces, such as exposed collagen during vascular injury. This activation triggers a series of reactions involving various clotting factors that culminate in the enhancement of fibrin formation. Thus, it is essential for developing a stable clot and ensuring that bleeding is effectively controlled.

In contrast, primary hemostasis involves the formation of the initial platelet plug, which does not require the activation of the coagulation factors. The vascular phase is characterized by vasoconstriction and exposure of the underlying collagen, while fibrinolysis refers to the process of clot breakdown after healing has occurred. Factor XII is not involved in these phases, confirming its critical role in secondary hemostasis.