In isolated and pathological states, blood is activated by thrombinogen to form thrombin, which converts fibrinogen to fibrin and causes blood to clot in vitro or form clots in vivo, while fibrinogen is activated to fibrinase, which degrades cross-linked fibrin and produces its specific degradation product, D-dimer. -dimer is significantly increased in thrombotic disease, deep venous thrombosis, acute myocardial infarction, pulmonary infarction, DIC, and also in the pre-thrombotic state. D-dimer has been widely used as an indicator of thrombolytic therapy, with increased levels in thrombosis and decreased levels in complete thrombosis. D-dimer is increased in secondary fibrinolysis and normal in primary fibrinolysis and is the main indicator to differentiate between the two.