D-dimer is increased at the onset of pulmonary embolism, and clinically the possibility of pulmonary embolism is considered when D-dimer is higher than 0.5 mg/L. However, in pulmonary embolism, there is no specific manifestation of increased D-dimer, and the general specificity is only about 40%. However, for the diagnosis of pulmonary embolism, the gold standard still relies on CTA or pulmonary angiography of the pulmonary artery. Therefore, when the patient’s D-dimer is elevated above 0.5mg/L, pulmonary embolism can only be highly suspected but not definitively diagnosed, and further CTA of the pulmonary artery is needed to confirm whether there is pulmonary embolism.