Objective:To explore the clinical value of arterial partial pressure of carbon dioxide (PaCO 2) combined with Wells score in predicting acute pulmonary embolism (PE). Methods:Patients with suspected acute PE admitted to Emergency Department of Beijing Chaoyang Hospital, Capital Medical University from January 1, 2016 to August 31, 2021 were screened. Patients with positive computed tomography pulmonary angiography (CTPA) results were classified as the PE group, and those with negative CTPA results were classified as the non-PE group. Demographic characteristics, symptoms, vital signs, underlying diseases, risk factors for venous thrombosis, arterial blood gas analysis and Wells scores were statistically analyzed and compared between the two groups, and the clinical efficacy of PaCO 2 combined with Wells score in predicting acute PE was evaluated. Results:A total of 1 869 patients with suspected acute PE were screened, and 1 492 patients were finally selected. There were 537 cases in the PE group and 955 cases in the non-PE group. The frequency of chest pain, dyspnea, unilateral lower limb edema, history of PE or deep venous thrombosis, history of surgery or immobilization within 3 months, history of fracture within 3 months, active malignant tumor, elevated Wells score and reduced PaCO 2 in the PE group was significantly higher than that in the non-PE group (all P< 0.05). The area under receiver operating characteristic (ROC) curve (AUC) of Wells score was 0.784 (95% CI: 0.758-0.810), and the sensitivity and specificity of predicting acute pulmonary embolism were 61.64% and 88.48%, respectively. The AUC of reduced PaCO 2 was 0.679 (95% CI: 0.651-0.707), and the sensitivity and specificity of predicting acute pulmonary embolism were 79.89% and 55.92%, respectively. The AUC of reduced PaCO 2 combined with Wells score was 0.837 (95% CI: 0.816-0.858), and the sensitivity and specificity of predicting acute pulmonary embolism were 74.12% and 77.07%, respectively. The AUC of reduced PaCO 2 combined with Wells score was significantly greater than the AUC of Wells score ( P<0.001) and the AUC of reduced PaCO 2 ( P<0.001). Conclusions:The efficacy of PaCO 2 reduction combined with Wells score in predicting acute PE was superior to that of either of them alone. This was a beneficial supplement to the screening of patients with acute PE, and would also help reduce the abuse of CTPA in the emergency department.