All patients underwent a sequential diagnostic workup, including clinical probability assessment, a rapid quantitative ELISA D-dimer test, venous compression ultrasonography of the lower limbs, ventilation-perfusion lung scan or helical CT scan, and angiography in case of an inconclusive noninvasive workup. In the first study,2 clinical probability was assessed implicitly, based on history, risk factors, physical examination, and laboratory tests available in the emergency department (chest radiograph, electrocardiogram, and arterial blood gas analysis). In the second study,5 the Geneva score (Table 113) was used for clinical assessment, and the score assessment could be overridden by implicit evaluation. Implicit evaluation, the Geneva score, and the Geneva score with clinical override have been shown to have a similar predictive accuracy for PE.14 A D-dimer level below the cutoff value of 500 μg/L ruled out PE. In patients with D-dimer levels above that value, lower limb venous compression ultrasonography was performed. Patients with a proximal DVT shown by compression ultrasonography were treated without further testing. Patients without a DVT proceeded to ventilation-perfusion lung scan in the first study2 and to helical CT scan in the second study.5 Finally, pulmonary angiography was performed in patients with a nondiagnostic ventilation-perfusion lung scan and an intermediate or high clinical probability (first study2) and in patients with a negative CT scan and a high clinical probability (second study5). Therefore, criteria for ruling out PE were a negative D-dimer test result (D-dimer level, <500 μg/L), a normal result on the ventilation-perfusion lung scan, the association of low clinical probability and a nondiagnostic ventilation-perfusion lung scan (first study), the association of a normal result on the helical CT scan in patients with low or intermediate clinical probability (second study), or a normal result on the angiogram. The 3-month thromboembolic risk in patients in whom PE was ruled out based on those criteria and were therefore not treated by anticoagulant agents was about 1%. Pulmonary embolism was established in the presence of a clinical suspicion of PE and a proximal DVT, a high-probability ventilation-perfusion lung scan, a pathologic result on the helical CT scan, or a pathologic result on the angiogram.