The goal of this prospective observational study is to explore the influencing factors of the efficacy and safety of anticoagulant therapy for pulmonary thromboembolism in special populations with older age, renal insufficiency or co-existing malignancy, and establish a predictive model to guide clinical practice. The main questions it aims to answer are:

• To analyze the influencing factors of the efficacy and safety of anticoagulant therapy for specific populations with pulmonary thromboembolism (PTE) in the real world (such as the elderly, those with impaired kidney function, and individuals with malignant tumors).
• Whether we can use machine-learning models to predict bleeding events and VTE recurrence in special populations following anticoagulant therapy in the real world? Participants will receive diagnostic and therapeutic measures for pulmonary thromboembolism in accordance with clinical guidelines, including anticoagulant therapy. Some patients need to have peripheral blood samples collected at the time of enrollment and 3 months after anticoagulant therapy.

Inclusion Criteria:

1. Age ≥ 18 years old;
2. Adult patients with objectively diagnosed pulmonary thromboembolism (PTE) (with or without concomitant deep vein thrombosis);
3. Specific populations meeting any of the following criteria: elderly patients (≥75 years old); patients with impaired kidney function (creatinine clearance estimated by the Cockcroft-Gault formula, CrCl < 60ml/min); patients with active malignancies (under treatment or with unrecovered malignancies);
4. Patients who have not started anticoagulant therapy before enrollment and are planned for anticoagulant treatment after evaluation by the attending physician;
5. Ecpected life expectancy longer than 3 months.
6. Patients who understand and agree to participate in this study, sign the informed consent form, and adhere to regular follow-up visits.

Exclusion Criteria:

1. Moderate or severe liver dysfunction (Child-Pugh class B or C);
2. Spontaneous bleeding tendency, such as coagulation disorders or thrombocytopenia (PLT<20×10^9/L);
3. Contraindications to anticoagulant drugs, including allergy to anticoagulants, clinically significant active bleeding, significant risk of major bleeding due to lesions or conditions, significantly abnormal coagulation function, liver disease with clinically relevant bleeding risk, thrombocytopenia, etc., as determined by the attending physician;
4. High-risk pulmonary embolism requiring thrombolysis;
5. Patients currently participating in other clinical trials.

Special populations of PTE patients who are elderly, have renal insufficiency, or have concomitant malignancies.