D-dimer is mainly used to detect fibrinolytic function. Elevated and positive D-dimer is seen in secondary fibrinolytic hyperfunction, which is mainly seen clinically in patients with hypercoagulable states, diffuse intravascular coagulation, renal disease and rejection after organ transplantation, and thrombolytic therapy. D-dimer is elevated whenever there is activated thrombus formation or fibrinolytic activity in the body’s blood vessels. In common clinical diseases, such as myocardial infarction, cerebral infarction, pulmonary embolism, formation of venous thrombosis, surgery, tumors, diffuse intravascular coagulation, tissue necrosis, and infection, can lead to elevated D-dimer. In elderly patients, because of diseases such as bacteraemia, which tends to cause clotting abnormalities, it can also lead to elevated D-dimer.