In the main, there are two explanations for the failure to diagnose pulmonary embolism: pulmonary embolism may be clinically silent, and there is no definitive, noninvasive diagnostic test. Indeed, ventilation perfusion lung scans are nondiagnostic in the majority of patients with suspected acute pulmonary embolism. Pulmonary angiography may be used to establish a diagnosis in such patients, but it is underutilized because of a mortality risk around 1 percent.