We designed a diagnostic strategy, based on clinical probability and D-dimer concentration, to select patients who were unlikely to have pulmonary embolism (PE), before further diagnostic workup was performed. The utility and safety of this strategy were evaluated in a prospective management study.
Consecutive patients with suspected PE had D-dimer testing and clinical probability assessment with a clinical decision rule. Patients with a low probability and a normal D-dimer concentration (<500 ng/mL) were considered not to have PE, and further diagnostic testing and anticoagulant therapy were withheld. In patients with a low probability and elevated D-dimer level or with a moderate or high probability, bilateral compression ultrasonography of the legs was performed. If deep venous thrombosis was detected, venous thromboembolism was diagnosed. If compression ultrasonography was normal, pulmonary angiography was performed. All patients were followed up for 3 months.
Of the 234 consecutive patients, 26% had the combination of a low probability and normal D-dimer level. During the follow-up period, none of these patients died and 3 patients had recurrent complaints of PE. In these 3 patients, PE was excluded by objective testing. The 3-month thromboembolic risk was therefore 0% (95% confidence interval, 0%-6%). The prevalence of PE in the entire population was 22%.
The combination of a low clinical probability and a normal D-dimer concentration appears to be a safe method to exclude PE, with a high clinical utility, and is readily accepted by clinicians.