title: Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study.
abstract: OBJECTIVE
  To measure the sensitivity of modern third generation computed tomography in emergency patients being evaluated for possible subarachnoid haemorrhage, especially when carried out within six hours of headache onset.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  11 tertiary care emergency departments across Canada, 2000-9.
  
  
  METHODS
  Neurologically intact adults with a new acute headache peaking in intensity within one hour of onset in whom a computed tomography was ordered by the treating physician to rule out subarachnoid haemorrhage.
  
  
  METHODS
  Subarachnoid haemorrhage was defined by any of subarachnoid blood on computed tomography, xanthochromia in cerebrospinal fluid, or any red blood cells in final tube of cerebrospinal fluid collected with positive results on cerebral angiography.
  
  
  RESULTS
  Of the 3132 patients enrolled (mean age 45.1, 2571 (82.1%) with worst headache ever), 240 had subarachnoid haemorrhage (7.7%). The sensitivity of computed tomography overall for subarachnoid haemorrhage was 92.9% (95% confidence interval 89.0% to 95.5%), the specificity was 100% (99.9% to 100%), the negative predictive value was 99.4% (99.1% to 99.6%), and the positive predictive value was 100% (98.3% to 100%). For the 953 patients scanned within six hours of headache onset, all 121 patients with subarachnoid haemorrhage were identified by computed tomography, yielding a sensitivity of 100% (97.0% to 100.0%), specificity of 100% (99.5% to 100%), negative predictive value of 100% (99.5% to 100%), and positive predictive value of 100% (96.9% to 100%).
  
  
  CONCLUSIONS
  Modern third generation computed tomography is extremely sensitive in identifying subarachnoid haemorrhage when it is carried out within six hours of headache onset and interpreted by a qualified radiologist.
authors.affiliation: Department of Emergency Medicine, University of Ottawa, Clinical Epidemiology Program, Ottawa Hospital Research Institute, ON, Canada. jperry@ohri.ca
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Perry
authors.forename: Ian G
authors.initials: IG
authors.lastname: Stiell
authors.forename: Marco L A
authors.initials: ML
authors.lastname: Sivilotti
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Bullard
authors.forename: Marcel
authors.initials: M
authors.lastname: Emond
authors.forename: Cheryl
authors.initials: C
authors.lastname: Symington
authors.forename: Jane
authors.initials: J
authors.lastname: Sutherland
authors.forename: Andrew
authors.initials: A
authors.lastname: Worster
authors.forename: Corinne
authors.initials: C
authors.lastname: Hohl
authors.forename: Jacques S
authors.initials: JS
authors.lastname: Lee
authors.forename: Mary A
authors.initials: MA
authors.lastname: Eisenhauer
authors.forename: Melodie
authors.initials: M
authors.lastname: Mortensen
authors.forename: Duncan
authors.initials: D
authors.lastname: Mackey
authors.forename: Merril
authors.initials: M
authors.lastname: Pauls
authors.forename: Howard
authors.initials: H
authors.lastname: Lesiuk
authors.forename: George A
authors.initials: GA
authors.lastname: Wells
mesh_terms: D000208:Acute Disease; D003951:Diagnostic Errors; D004636:Emergency Service, Hospital; D005260:Female; D020773:Headache Disorders / Q000209:etiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013345:Subarachnoid Hemorrhage / Q000000981:diagnostic imaging*; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome