When fibrin fibers are split, fragments called D-dimers are formed. When determining the content of D-dimers using specific antisera, it is possible to judge the extent to which fibrinolysis, but not fibrogenolysis, is expressed in the blood being tested. An increased content of D-dimer is one of the main markers of hemostasis system activation, since it reflects both the formation of fibrin in the blood being tested and its lysis.