D-dimer is gaining importance as an indicator of dysregulation of coagulation and fibrinolytic balance. When coagulation occurs in the body, thrombin acts on fibrinogen and converts it into cross-linked fibrin, while the fibrinolytic system is activated and degrades the cross-linked fibrin to form various FDP fragments. As a result of the cross-linking of the r-chain, two D-fragments containing the r-chain are created, i.e. D-dimers. D-dimer mainly reflects fibrinolytic function, and increased or positive is seen in secondary fibrinolytic hyperfunction, such as hypercoagulable state, diffuse intravascular coagulation, renal disease, organ transplant rejection, thrombolytic therapy, etc. D-dimer is elevated whenever there is activated thrombus formation and fibrinolytic activity in the body’s blood vessels. Myocardial infarction, cerebral infarction, pulmonary embolism, venous thrombosis, surgery, liver disease and malignancy, diffuse intravascular coagulation, infection and tissue necrosis can all lead to elevated D-dimer. Especially in elderly people and hospitalized patients, diseases such as bacteraemia can cause clotting abnormalities and lead to elevated D-dimer. However, this test can be positive for any bleeding with clot formation, so its specificity is low and sensitivity is high. According to the study, plasma D-dimer results were significantly higher in cerebrovascular patients than in normal controls (P<0.01), where the acute phase of ischemic stroke was again significantly higher than the recovery phase (P<0.01), while it was not elevated in stroke recovery, the same as in healthy elderly controls (P>0.05). Changes in plasma D-dimer concentrations were age-related, with a large difference between patients in the older age group ≥75 years and normal subjects, while the difference was not significant in the lower age group. D-dimer can be used as a specific monitoring index for thrombolytic therapy in thrombotic diseases: in thrombolytic therapy, the change of D-dimer level generally has the following characteristics: ① the D-dimer level increases significantly in a short period of time after thrombolysis, and then decreases gradually, suggesting effective treatment; ② the D-dimer level continues to increase or decreases slowly after thrombolysis, suggesting insufficient dosage of thrombolytic drugs; ③ thrombolytic therapy should be continued until the D-dimer (3) Thrombolytic therapy should be continued until the D-dimer level decreases to the normal range. In addition, the change of D-dimer should be observed regularly for a period of time after thrombolytic therapy to prevent recurrence of thrombosis. Therefore, dynamic detection of D-dimer concentration changes before, during and after thrombolysis is of great clinical value to monitor the effect of thrombolytic drugs.