Background: We designed a prospective multicentre outcome study to evaluate a diagnostic strategy based on clinical probability, spiral CT, and venous compression ultrasonography of the legs in patients with suspected pulmonary embolism (PE). The main aim was to assess the safety of withholding anticoagulant treatment in patients with low or intermediate clinical probability of PE and negative findings on spiral CT and ultrasonography.
Methods: 1041 consecutive inpatients and outpatients with suspected PE were included. Patients with negative spiral CT and ultrasonography and clinically assessed as having a low or intermediate clinical probability were left untreated. Those with high clinical probability underwent lung scanning, pulmonary angiography, or both. All patients were followed up for 3 months.
Findings: PE was diagnosed in 360 (34.6%) patients; 55 had positive ultrasonography despite negative spiral CT. Of 601 patients with negative spiral CT and ultrasonography, 76 were clinically assessed as having a high probability of PE; lung scanning or angiography showed PE in four (5.3% [95% CI 1.5-13.1]). The remaining 525 patients were assessed as having low or intermediate clinical probability, and 507 of them were not treated. Of these patients, nine experienced venous thromboembolism during follow-up (1.8% [0.8-3.3]). The diagnostic strategy proved inconclusive in 95 (9.1%) patients, and pulmonary angiography was done in 74 (7.1%).
Interpretation: Withholding of anticoagulant therapy is safe when the clinical probability of PE is assessed as low or intermediate and spiral CT and ultrasonography are negative.