title: Prospective study of the diagnostic accuracy of the simplify D-dimer assay for pulmonary embolism in emergency department patients.
abstract: OBJECTIVE
  To determine if a d-dimer assay (Simplify D-dimer; Agen Biomedical; Brisbane, Australia) can reliably exclude pulmonary embolism (PE) by producing a posttest probability of PE < 1% in low-risk, symptomatic emergency department (ED) patients.
  
  
  METHODS
  Hemodynamically stable patients were evaluated for PE using a structured d-dimer-centered protocol; d-dimer testing was performed prior to imaging. Prior to testing, physicians completed an electronic data form that included their unstructured clinical estimate for the pretest probability of PE (< 15%, 15 to 40%, or > 40%) and the elements of the Charlotte rule and Canadian score for PE. Criterion standard was selective use of pulmonary vascular imaging and 90-day follow-up.
  
  
  RESULTS
  We enrolled 2,302 patients (mean age, 45 +/- 16 years [+/- SD]; 31% male); 108 patients received a diagnosis of PE (4.7%; 95% confidence interval [CI], 3.6 to 5.6%). The overall sensitivity and specificity of the d-dimer assay were 80.6% (95% CI, 71.8 to 87.5%) and 72.5% (95% CI, 70.6 to 74.4%), respectively. The negative likelihood ratio and negative predictive value were 0.27 (95% CI, 0.18 to 0.39) and 98.7% (95% CI, 98.0 to 99.1%), respectively. The posttest prevalence of PE among low-risk patients with negative d-dimer results was 0.7% (95% CI, 0.3 to 1.4%) for the unstructured estimate, 1.2% (95% CI, 0.7 to 2.0%) for the Canadian score, and 1.1% (95% CI, 0.6 to 1.7%) for the Charlotte rule.
  
  
  CONCLUSIONS
  The Simplify D-dimer assay had moderate sensitivity and relatively high specificity for PE in low-risk ED patients. The combination of a physician's unstructured estimate of pretest probability of PE of < 15% and a negative d-dimer result produced a posttest probability of PE of 0.7% (95% CI, 0.3 to 1.4%).
authors.affiliation: Director, Emergency Medicine Research, Department of Emergency Medicine, Carolinas Medical Center, PO Box 32861, Charlotte, NC 28323-2861, USA. jkline@carolinas.org
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Kline
authors.forename: Michael S
authors.initials: MS
authors.lastname: Runyon
authors.forename: William B
authors.initials: WB
authors.lastname: Webb
authors.forename: Alan E
authors.initials: AE
authors.lastname: Jones
authors.forename: Alice M
authors.initials: AM
authors.lastname: Mitchell
mesh_terms: D000328:Adult; D004636:Emergency Service, Hospital; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000378:metabolism*; D006801:Humans; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000097:blood / Q000175:diagnosis*; D015203:Reproducibility of Results
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D