title: Computed tomographic pulmonary angiography and pulmonary embolism: predictive value of a d-dimer assay.
abstract: BACKGROUND
  Computed tomographic pulmonary angiography (CTPA) is increasingly being used as first investigation for suspected pulmonary embolism (PE). The investigation has high predictive value, but is resource and time intensive and exposes patients to considerable radiation. Our aim was to assess the potential value of a negative d-dimer assay to exclude pulmonary emboli and reduce the number of performed CTPAs.
  
  
  METHODS
  All CTPAs performed in a Scottish secondary care hospital for a fourteen month period were retrospectively reviewed. Collected data included the presence or absence of PE, d-dimer results and patient demographics. PE positive CTPAs were reviewed by a specialist panel.
  
  
  RESULTS
  Pulmonary embolisms were reported for 66/405 (16.3%) CTPAs and d-dimer tests were performed for 216 (53%). 186/216 (86%) patients had a positive and 30 (14%) a negative d-dimer result. The panel agreed 5/66 (7.6%) false positive examinations. The d-dimer assay's negative predictive value was 93.3% (95% CI = 76.5%-98.8%) based on the original number of positive CTPAs and 100% (95% CI = 85.9%-100%) based on expert review. Significant non-PE intrapulmonary pathology was reported for 312/405 (77.0) CTPAs, including 13 new diagnoses of carcinoma.
  
  
  CONCLUSIONS
  We found that a low d-dimer score excluded all pulmonary embolisms, after a further specialist panel review identified initial false positive reports. However, current evidence-based guidelines still recommend that clinicians combine a d-dimer result with a validated clinical risk score when selecting suitable patients for CTPA. This may result in better use of limited resources, prevent patients being exposed to unnecessary irradiation and prevent potential complications as a result of iodinated contrast.
authors.affiliation: Radiology Department, Glasgow Royal Infirmary, 84 Castle Street, Glasgow G4 0SF, UK. patdeo75@yahoo.co.uk
authors.forename: Patricia
authors.initials: P
authors.lastname: Deonarine
authors.forename: Carl
authors.initials: C
authors.lastname: de Wet
authors.forename: Alistair
authors.initials: A
authors.lastname: McGhee
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000792:Angiography; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis*; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011651:Pulmonary Artery / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D011655:Pulmonary Embolism / Q000097:blood* / Q000175:diagnosis* / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D063127:Secondary Health Care; D014057:Tomography, X-Ray Computed
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D