Coagulation factors are pro-coagulant substances contained in blood plasma, also known as clotting factors, and at least 16 of them exist. The official names were given using Roman numerals in the order in which they were discovered, such as factor II and factor VII. Factor IV was later discovered to be calcium ion and factor VI to be activated factor V, leading to the elimination of the nomenclature of factor IV and factor VI. Most coagulation factors are synthesized in the liver, and a few are synthesized in endothelial cells and other locations. Among them, the synthesis of factor II, factor VII, factor IX and factor X requires the participation of vitamin K, also known as vitamin K-dependent coagulation factors. The reference interval for the activity of most coagulation factors in the organism is between 50% and 150%. Fibrinogen, i.e., factor I, is determined by the Krauss method for functional fibrinogen. Fibrinogen is converted into soluble fibrin monomers by the action of thrombin, and in the presence of factor XIII and calcium ions into a cross-linked fibrin network, which ultimately acts as a hemostatic agent.