D-dimer is a specific degradation product of cross-linked fibrin in the human body, which is negative in normal subjects, with concentrations not exceeding 200 μg/L. An increase in D-dimer is indicative of secondary fibrinolysis, and is often used clinically as a basis for the diagnosis of diseases such as pulmonary embolism and deep vein thrombosis. When these diseases occur, there is a significant increase in D-dimer, as well as in various thrombotic diseases, such as myocardial infarction and cerebral thrombosis. When thrombotic diseases are treated with thrombolytic therapy, D-dimer may also increase significantly. In addition, diffuse intravascular coagulation and intravascular coagulation caused by various diseases may also show a significant increase in D-dimer, and the higher the D-dimer, the more serious the condition.