title: Is the combination of negative computed tomography result and negative lumbar puncture result sufficient to rule out subarachnoid hemorrhage?
abstract: OBJECTIVE
  Current clinical practice assumes a negative computed tomography (CT) head scan result and a negative lumbar puncture result together are adequate to rule out subarachnoid hemorrhage in patients with acute headache. Our objective is to determine the sensitivity of a negative CT result combined with a negative lumbar puncture result to exclude subarachnoid hemorrhage.
  
  
  METHODS
  This prospective cohort study was conducted at 2 tertiary care emergency departments (EDs) during 3 years. We enrolled all patients who were older than 15 years, had a nontraumatic acute headache and normal neurologic examination result, and who had a CT head scan and a lumbar puncture if the CT result was negative (ie, no blood in the subarachnoid space). Patients were followed up with a structured telephone questionnaire 6 to 36 months after their ED visit and electronic hospital records review to ensure no missed subarachnoid hemorrhage. We calculated sensitivity, specificity, and likelihood ratios of the strategy of CT and then lumbar puncture for subarachnoid hemorrhage.
  
  
  RESULTS
  Five hundred ninety-two patients were enrolled, including 61 with subarachnoid hemorrhage. The mean patient age was 43.6 years, with 59.1% female patients. All cases of subarachnoid hemorrhage were identified on initial CT or lumbar puncture. One patient without subarachnoid hemorrhage was subsequently diagnosed with cerebral aneurysm, requiring surgery. The strategy classified patients with subarachnoid hemorrhage with sensitivity, specificity, and positive and negative likelihood ratios (with 95% confidence intervals [CIs]) of 100% (95% CI 94% to 100%), 67% (95% CI 63% to 71%), 3.03 (95% CI 2.69 to 3.53), and 0. For diagnosis of subarachnoid hemorrhage or aneurysm, these were 98% (95% CI 91% to 100%), 67% (95% CI 63% to 71%), 2.98 (95% CI 2.63 to 3.38), and 0.02 (95% CI 0.00 to 0.17), respectively.
  
  
  CONCLUSIONS
  To our knowledge, this is the largest prospective study evaluating the accuracy of a strategy of CT and lumbar puncture to rule out subarachnoid hemorrhage in alert ED patients with an acute headache. This study validates clinical practice that a negative CT with a negative lumbar puncture is sufficient to rule out subarachnoid hemorrhage.
authors.affiliation: Department of Emergency Medicine, University of Ottawa, Ottawa, Ontario, Canada. jperry@ohri.ca
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Perry
authors.forename: Alena
authors.initials: A
authors.lastname: Spacek
authors.forename: Melissa
authors.initials: M
authors.lastname: Forbes
authors.forename: George A
authors.initials: GA
authors.lastname: Wells
authors.forename: Melodie
authors.initials: M
authors.lastname: Mortensen
authors.forename: Cheryl
authors.initials: C
authors.lastname: Symington
authors.forename: Nicole
authors.initials: N
authors.lastname: Fortin
authors.forename: Ian G
authors.initials: IG
authors.lastname: Stiell
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016001:Confidence Intervals; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013129:Spinal Puncture; D013345:Subarachnoid Hemorrhage / Q000175:diagnosis* / Q000000981:diagnostic imaging; D011795:Surveys and Questionnaires; D014057:Tomography, X-Ray Computed / Q000379:methods*