Study objective: We derive a decision rule to partition emergency department patients with suspected pulmonary embolism (PE) into a small, high-risk group (>40% pretest probability) that is unsafe for D -dimer testing and a larger group that is safe to have PE ruled out with either a whole-blood D -dimer plus alveolar deadspace measurement or a quantitative D -dimer assay.
Methods: Nine hundred thirty-four patients with suspected PE were studied at 7 urban EDs in the United States. Patients were prospectively interviewed and examined for recognized symptoms, signs, and risk factors associated with PE. These data were collected before standard objective imaging for PE. Selected variables were analyzed by multivariate logistic analysis to determine factors associated with PE (P <.05). A decision rule was then constructed to categorize approximately 80% of ED patients as safe for D -dimer testing.
Results: Pretest prevalence of PE was 19.4% (181/934; 95% confidence interval [CI] 16.3% to 21.7%). Six variables found to be significant on multivariate analysis were used to construct the decision rule. Unsafe patients had either a shock index (heart rate/systolic blood pressure) more than 1.0 or age older than 50 years, together with any one of the following conditions: unexplained hypoxemia (SaO (2) <95%; no prior lung disease), unilateral leg swelling, recent major surgery, or hemoptysis. These criteria were met by 197 (21.0%) of 934 patients, and 83 of 197 (42.1%; 95% CI 35.3% to 49.6%) patients had PE. Exclusion of these 197 unsafe patients significantly decreased the probability of PE in the remaining 737 (79.0%) safe patients to 13.3% (95% CI 10.9% to 15.9%).
Conclusion: Simple clinical criteria can permit safe D -dimer testing in the majority of ED patients with suspected PE. These criteria warrant prospective validation.