STUDY OBJECTIVE: The literature suggests that the d -dimer is useful in patients 
suspected of having pulmonary embolism and who have a low pretest probability of 
disease. A previously defined clinical decision rule, the Wells Criteria, may 
provide a reliable and reproducible means of determining this pretest 
probability. We evaluate the interrater agreement and external validity of Wells 
Criteria in determining pretest probability in patients suspected of having 
pulmonary embolism.
METHODS: This was a prospective observational study. Trained research assistants 
enrolled patients during 120 random 8-hour shifts. Patients who underwent 
imaging for pulmonary embolism after a medical history, physical examination, 
and chest radiograph were enrolled. Treating providers and research assistants 
determined pretest probability according to Wells Criteria in a blinded fashion. 
Two d -dimer assays were run. Three-month follow-up for the diagnosis of 
pulmonary embolism was performed. Interrater agreement tables were created. 
kappa Values, sensitivities, and specificities were determined.
RESULTS: Of the 153 eligible patients, 3 patients were missed, 16 patients 
declined, and 134 (88%) patients were enrolled. Sixteen (12%) patients were 
diagnosed with pulmonary embolism. The kappa values for Wells Criteria were 0.54 
and 0.72 for the trichotomized and dichotomized scorings, respectively. When 
Wells Criteria were trichotomized into low pretest probability (n=59, 44%), 
moderate pretest probability (n=61, 46%), or high pretest probability (n=14, 
10%), the pulmonary embolism prevalence was 2%, 15%, and 43%, respectively. When 
Wells Criteria were dichotomized into pulmonary embolism-unlikely (n=88, 66%) or 
pulmonary embolism-likely (n=46, 34%), the prevalence was 3% and 28%, 
respectively. The immunoturbidimetric and rapid enzyme-linked immunosorbent 
assay d -dimer assays had similar sensitivities (94%) and specificities (45% 
versus 46%).
CONCLUSION: Wells Criteria have a moderate to substantial interrater agreement 
and reliably risk stratify pretest probability in patients with suspected 
pulmonary embolism.