Prolonged prothrombin time, mainly reflecting exogenous coagulation factors and common pathway coagulation factor deficiency, can be seen in the following situations: 1. Coagulation factor deficiency: it can cause prolonged PT results, i.e. prolonged prothrombin time results; 2. Congenital coagulation factor deficiency: in endogenous and common pathway, congenital deficiency of a particular coagulation factor can cause prolonged prothrombin time; 3. Presence of anticoagulant in the blood substance: for example, in lupus erythematosus, the presence of anticoagulant substances can cause prolongation of prothrombin time; 4, advanced DIC: prothrombin time can also be prolonged; 5, hypofibrinogenemia: fibrinogen deficiency and common pathway coagulation factor deficiency can cause prolongation of coagulation results.