Usually when the D-dimer level is higher than 500 ng/ml, it is necessary to consider the presence of thrombus formation in the human body. 1. D-dimer is the product of decomposition of fibrin in human body, fibrin is the main substance of human body to promote coagulation, elevated fibrin in human body can easily lead to the occurrence of thrombus, so D-dimer can be used in clinic to reflect whether thrombus is formed in human body. 2. D-dimer usually reflects the body’s coagulation and fibrinolytic ability, but also can reflect whether the body has thrombosis and other conditions, so in the clinic should be alert to the elevation of dimer. However, elevated dimers do not necessarily mean thrombosis, but may also be elevated in cases of bleeding or trauma. 3. D-dimer can only reflect the body’s coagulation and anticoagulation system, not always caused by thrombosis, and should be combined with the patient’s clinical manifestations to make a diagnosis.