The predominant clinical feature of both genetic predisposition to thrombosis and acquired hypercoagulable states is a tendency to thrombosis, mostly in the form of venous thromboembolic disease (VTE), with an increased incidence of arterial thrombosis in some diseases. Patients with acquired hypercoagulable states develop thrombosis on the basis of primary disease. In contrast, patients with hereditary thrombophilia have a lifelong tendency to thrombosis, with VTE predominating, and some hereditary thrombophilia (e.g., hyperhomocysteinemia) is associated with an increased risk of arterial thrombosis. VTE includes: 1. Deep vein thrombosis Deep vein thrombosis (DVT) occurs most often in the lower extremities, but can also occur in other parts of the body. Asymmetric swelling, pain and superficial varicose veins in the lower extremities are the three main symptoms of DVT in the lower extremities. The site of venous thrombosis can be initially estimated based on the plane of swelling in the lower extremities. Bilateral lower extremity edema is suggestive of inferior vena cava thrombosis. The nature of pain is cramping or dull pain. Superficial varicose veins are a sign of increased venous pressure and establishment of collateral circulation. Some lower extremity DVT has no obvious clinical manifestations, called “silent” DVT. mesenteric vein thrombosis may present with clinical manifestations similar to those of acute abdomen. 2, pulmonary embolism pulmonary embolism (PE) is the main serious complication of lower extremity DVT, which can cause sudden death of patients in serious cases. The triad of hemoptysis, chest pain and dyspnea was once considered as the main clinical clue for the diagnosis of pulmonary embolism, but in fact, the performance of most patients is not typical. If a patient with lower extremity DVT presents with chest tightness, shortness of breath, hemoptysis, or sudden syncope, the possibility of pulmonary embolism should be highly considered. Pulmonary embolism may also present with pneumonia and pleural effusion, as well as manifestations resembling angina pectoris or even myocardial infarction. Patients with “silent” DVT may have pulmonary embolism as the first manifestation.