The goal of this observational study is to systematically analyze the relationship between trough/peak concentrations of novel oral anticoagulants (NOACs) and antiplatelet drugs with clinical events, aiming to provide high-level evidence for therapeutic drug monitoring (TDM) and personalized dosing.The main questions it aims to answer are:

• What are the optimal preventive and therapeutic concentration ranges for different NOACs (rivaroxaban, apixaban, dabigatran, edoxaban) and antiplatelet drugs (aspirin, indobufen)?
• What are the key factors influencing the blood drug concentrations of NOACs and antiplatelet drugs (such as liver and kidney function, age, weight, concomitant medications)?
• How can we establish a model to predict blood drug concentrations of NOACs and antiplatelet drugs and their related clinical events? Participants will receive routine clinical care. During treatment, blood samples will be regularly collected to measure patients' blood drug concentrations (Ctrough and Cmax), and clinical responses and adverse events will be recorded.

Inclusion criteria:

• Age ≥ 8 years old;
• Diagnosed with one of the following diseases and in need of long - term anticoagulant therapy: non - valvular atrial fibrillation (CHA₂DS₂ - VA score ≥ 1); venous thromboembolism (deep vein thrombosis or pulmonary embolism); having other indications for using NOACs to prevent and treat thrombotic diseases;
• Currently receiving NOAC treatment (rivaroxaban, apixaban, dabigatran etexilate, edoxaban);
• Willing and able to comply with the requirements of the research protocol and the follow - up plan;
• Signed the informed consent form.
• Age ≥ 18 years old;
• Assessed as patients at high risk of bleeding within 72 hours after the onset of symptoms;
• Receiving indobufen treatment for the first time after admission;
• Willing and able to comply with the requirements of the research protocol and the follow - up plan;
• Signed the informed consent form.

Exclusion criteria:

• Having contraindications to the use of NOACs or being allergic to NOACs;
• Having been enrolled in other clinical trials.
• Being allergic to or having contraindications to indobufen;
• Needing to change antithrombotic drugs or combine with other antiplatelet/anticoagulant therapies (such as clopidogrel, ticagrelor, warfarin, heparin, etc.) during the study;
• Cardiogenic stroke or stroke induced by angioplasty/vascular surgery;
• Having a history of aneurysm (intracranial or peripheral);
• Severe abnormal liver and kidney functions;
• Pregnant, lactating women or women of childbearing age who are unwilling to take effective contraceptive measures;
• Life expectancy < 1 year;
• Mental or emotional disorders preventing cooperation with follow - up;
• Participating in other clinical trials within 30 days before enrollment;
• Unable to complete blood concentration detection (such as difficulty in establishing venous access).

The study enrolls two distinct patient populations:

Thrombotic Disease Patients (4,000 subjects):

Age ≥ 8 years

Diagnosed with one of the following conditions requiring long-term anticoagulation:

Non-valvular atrial fibrillation (CHA₂DS₂-VA score ≥ 1) Venous thromboembolism (deep vein thrombosis or pulmonary embolism) Other indications for NOACs in thrombotic disease prevention/treatment Currently receiving NOAC therapy (rivaroxaban, apixaban, dabigatran, or edoxaban) Willing and able to comply with study protocol and follow-up schedule Signed informed consent

Ischemic Stroke Patients (1,000 subjects):

Age ≥ 18 years Assessed as high bleeding risk within 72 hours after symptom onset First-time treatment with indobufen after hospital admission Willing and able to comply with study protocol and follow-up schedule Signed informed consent