The Chinese name for APTT is Activated Partial Thromboplastin Time. an abnormality of the APTT test is that the APTT time value is in most cases greater than the normal range value. When a patient has any of the following abnormalities, the APTT time value will appear prolonged and a greater than normal range APTT time value will be seen detected on the test sheet. 1. If one or more of them has a decrease in coagulation factors, but not significantly, there will be easy bleeding after injury and the APTT time value will be prolonged accordingly; if there is a significant decrease in coagulation factors, there is a risk of spontaneous bleeding and the APTT time value will be significantly prolonged. These coagulation factors include coagulation factor VIII (FⅧ), coagulation factor IX (FIX), and coagulation factor D (FD). In clinical practice, hemophilia A is a congenital decrease in FⅧ, hemophilia B is a congenital decrease in FIX, and hemophilia C is a congenital decrease in FⅪ. In congenital hemophilia, hemophilia A accounts for 80%, hemophilia B accounts for 20%, and in China, hemophilia C is rare. 2. When any of the following contact activating factors in the coagulation process are insufficient, they will also lead to prolonged APTT, but their deficiency, will not lead to bleeding. They are coagulation factor Ⅻ (F Ⅻ), prokinetic peptide releasing enzyme (PK), and high molecular kininogen (HK). In clinical, pre-kinin releasing enzyme, high molecular kininogen decrease is rare. 3. Some abnormal auto-anticoagulant substances can also cause prolonged APTT. At present, the easily seen ones are FⅧ inhibitor, lupus anticoagulant (lupus antibody), antiphospholipid antibody, anti-β2-glycoprotein I antibody and antinuclear antibody. If FⅧ inhibitors are present, they lead to a decrease in FⅧ and the APTT must be prolonged. The clinical presentation is similar to that of FⅧ reduction. If FⅧ is significantly reduced, spontaneous bleeding may occur, similar to the condition of hemophilia A. The presence of other auto-anticoagulant substances in the body, such as lupus anticoagulant, antiphospholipid antibody, anti-β2-glycoprotein I antibody and antinuclear antibody, will not cause APTT prolongation in most cases, and in a few cases, will cause APTT prolongation. And these auto-anticoagulant substances cause APTT prolongation, which may cause serious bleeding. 4, heparin, or heparin-like drugs present in the body. It can cause APTT prolongation, which can cause bleeding.