Clinical significance of changes in D-dimer levels: 1. In DIC, extensive microthrombosis, as well as secondary hyperfibrinolysis, result in significantly higher D-dimer levels, which are significantly more sensitive and specific than screening assay tests such as platelet count, fibrinogen quantification, and fibrin(pro)degradation products (FDP). 2. In leukemia, leukemic cells contain strong pro-coagulant substances that act similarly to tissue clotting factors and activate the exogenous coagulation system. For example, the asplenophilic granules of M3 leukemia promyelocytes contain a large amount of proteolytic enzymes, and when the cells are destroyed, they are released into the blood stream, which can directly activate factor X, leading to a hypercoagulable state and thrombosis. Intense chemotherapy or radiation therapy kills a large number of leukemic cells, which causes the release of procoagulant substances contained in the leukemic cells into the bloodstream, leading to hypercoagulability and thrombosis. Plasma D-dimer levels in these patients can reach 20,000 μg/L or higher. In most patients, D-dimer levels fall to lower levels with treatment and lower levels of leukemic cells. As the number of leukemic cells in the peripheral blood decreases, D-dimer levels gradually decrease. The vast majority of patients with leukemia form DIC, and very few have venous thrombosis. The level of D-dimer is elevated in leukemia patients at the early stage of the disease and decreases after chemotherapy. Dynamic observation of the changes of D-dimer level in the plasma of patients can help to judge the disease and observe the efficacy of treatment. 3, acute myocardial infarction and cerebral thrombosis, the plasma D-dimer level is significantly increased in patients with acute onset, D-dimer test can be used not only as an indicator to observe the condition of myocardial infarction, but also as an ideal test method to observe thrombolytic therapy. 4, malignant solid tumors, according to statistics, the incidence of thrombosis in patients with malignant tumors is about 10-30%, among which the incidence of thrombosis complicated by adenocarcinoma is the highest, including pancreatic cancer, bronchial and lung cancer, gastric cancer, ovarian cancer, prostate cancer, colon cancer, kidney cancer, bladder cancer, malignant histiocytoma. The incidence of postoperative thrombosis (especially lower extremity venous thrombosis and pulmonary embolism) in cancer patients can be as high as 50%, with 90% of these patients having elevated D-dimer levels. In general, the level of D-dimer in malignant tumors is significantly higher than that in benign tumors, and the formed thrombus is mostly venous thrombosis, and a few of them are DIC. The plasma D-dimer test for patients with malignant tumor has a very important reference value for the diagnosis of patients with DIC and thrombosis. 5.After surgery, the activation of the coagulation system after tissue damage can lead to a significant increase in D-dimer level. In addition, besides tissue damage can lead to a tendency of thrombosis, if the patient has hereditary anticoagulation defects, or if risk factors exist, venous thrombosis is likely to occur, leading to a significant increase in D-dimer level. 6, D-dimer levels are increased in the physiological hypercoagulable state of late normal pregnancy, and plasma D-dimer levels are significantly higher in pregnant women than in non-pregnant women (p<0.05), but lower than in pregnant women with hyperemesis (p<0.05). The determination of plasma D-dimer levels is important for the diagnosis, efficacy detection and prognosis determination of hypercoagulable state in patients with hyperemesis. 7, In pulmonary embolism, D-dimer level was significantly increased, and the area of embolism as well as the size of the embolus was significantly correlated with D-dimer level. 8.In liver disease, it was found that the plasma D-dimer level was significantly increased in patients with liver disease and was positively correlated with the severity of liver disease. 9, D-dimer levels were significantly increased in secondary hyperfibrinolysis, and not in primary fibrinolysis. In old thrombosis, D-dimer is not increased. 10.D-dimer level is increased in tissue injury, and the magnitude of the increase in D-dimer level is related to the time and degree of injury. 11.Both acute blood loss and chronic blood loss lead to increased D-dimer levels. 12, Prolonged bed rest, oral contraceptives, and hereditary anticoagulation system defects can lead to deep vein thrombosis and significantly increased D-dimer levels. 13.In diabetes, D-dimer level is significantly increased when there is extensive thrombotic lesion. 14, deep vein thrombosis (DVT), almost all patients with DVT D-dimer positive, plasma D-dimer negative can basically exclude the possibility of DVT. d-dimer can reflect the changes in thrombus size, so it can be used as a guide for thrombolytic therapy and heparin anticoagulation and efficacy observation: persistently high during treatment, indicating that the treatment is ineffective; the level is elevated again, indicating the reoccurrence of thrombosis. 15. In nephrotic syndrome and renal failure, D-dimer level can be significantly increased.