From January 1, 2023 to December 30, 2023, patients who were suspected of pulmonary embolism and underwent CTPA examination at Nanyang Hospital of Southern Medical University were divided into pulmonary embolism group and non pulmonary embolism group. 1. Collect relevant data, including gender, age, primary disease, CTPA imaging and reports, BNP, troponin, electrocardiogram, cardiac ultrasound, PT, APTT, TT, fibrinogen, D-dimer, etc., and analyze demographic data, pulmonary embolism risk grading, APTT/fibrinogen ratio, and determine their cut-off values through statistical analysis of the two groups. 2. Follow up on the APTT/fibrinogen ratio after anticoagulation treatment and bleeding in the pulmonary embolism group.