"Coagulation also referred to as clotting, is that the process by which blood changes from a liquid to a gel, forming a grume. It potentially leads to hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism of coagulation involves activation, adhesion, and aggregation of platelets, also as deposition and maturation of fibrin.

Coagulation begins almost instantly after an injury to the vessel has damaged the endothelium lining the vessel. Exposure of blood to the subendothelial space initiates two processes: changes in platelets, and therefore the exposure of subendothelial tissue factor to plasma proconvertin, which ultimately results in cross-linked fibrin formation. Platelets immediately form a plug at the location of injury; this is often called primary hemostasis. Secondary hemostasis occurs simultaneously: additional coagulation (clotting) factors beyond proconvertin (listed below) respond during a cascade to make fibrin strands, which strengthen the platelet plug."