The fibrinolytic system is the most important anticoagulation system in the body. During lysis, thrombin hydrolyzes fibrin, releasing soluble fibrin monomers, which, under the action of factor xIIIa, form stable cross-linked fibrin. In late stages of disseminated intravascular coagulation, the fibrinolytic system is activated due to intravascular coagulation, resulting in secondary fibrinolysis and more pronounced bleeding symptoms. What are the symptoms that are easily confused with secondary enhanced fibrinolysis? Plasma D-dimer which is a specific product of fibrin degradation, measurement of plasma D-dimer can determine whether fibrin has been produced, thus providing an important basis for differentiating primary and secondary hyperfibrinolysis. Qualitative test: negative quantitative test: <400μg/L. In primary hyperfibrinolysis, fibrinogen is degraded before it is converted into fibrin in large quantities, and D-dimer is negative or not elevated; in secondary hyperfibrinolysis, such as thrombophilia and DIC, due to the enhanced coagulation mechanism in the pre-disease period, fibrin is produced in large quantities, which then causes hyperfibrinolysis, and therefore D-dimer is positive or significantly elevated. -dimer is positive or significantly elevated. Fasting venous blood is usually collected in a quiet state. Prolonged prothrombin time is prolonged when there is a significant decrease in fibrinogen or an increase in fibrin(pro)degradation products (FDP), but the results of the measurement can be influenced by heparin therapy. The use of continuous prothrombin time is a more sensitive indicator for the diagnosis of FDP. Plasma snake venom coagulation time was measured using an enzyme derived from snake venom (Reptilase) instead of thrombin. When FDP is increased, the coagulation time is prolonged and this method has the advantage of being unaffected by heparin.