title: Nontraumatic subarachnoid hemorrhage in the setting of negative cranial computed tomography results: external validation of a clinical and imaging prediction rule.
abstract: OBJECTIVE
  Clinical variables can reliably exclude a diagnosis of nontraumatic subarachnoid hemorrhage in patients with negative cranial computed tomography (CT) results. We externally validated 2 decision rules with 100% reported sensitivity for a diagnosis of subarachnoid hemorrhage, among patients undergoing lumbar puncture after a negative cranial CT result: (1) clinical rule: presence of any combination of age 40 years and older, neck pain or stiffness, loss of consciousness, or headache onset during exertion; and (2) imaging rule: cranial CT performed within 6 hours of headache onset.
  
  
  METHODS
  This was a matched case-control study of patients presenting to 21 emergency departments between 2000 and 2011. Patients with a diagnosis of subarachnoid hemorrhage as determined by lumbar puncture after a negative cranial CT result were screened for inclusion. A matched control cohort was selected among patients with a diagnosis of headache after negative cranial CT and lumbar puncture results.
  
  
  RESULTS
  Fifty-five cases of subarachnoid hemorrhage meeting inclusion criteria were identified, 34 (62%) of which were attributed to cerebral aneurysms. External validation of the clinical rule demonstrated a sensitivity of 97.1% (95% confidence interval [CI] 88.6% to 99.7%), a specificity of 22.7% (95% CI 16.6% to 29.8%), and a negative likelihood ratio of 0.13 (95% CI 0.03 to 0.61) for a diagnosis of subarachnoid hemorrhage. External validation of the imaging rule revealed that 11 of 55 subarachnoid hemorrhage cases (20%) had negative cranial CT results for tests performed within 6 hours of headache onset.
  
  
  CONCLUSIONS
  The clinical rule demonstrated useful Bayesian test characteristics when retrospectively validated against this patient cohort. The imaging rule, however, failed to identify 20% of subarachnoid hemorrhage patients with a negative cranial CT result.
authors.affiliation: Department of Emergency Medicine, Kaiser Permanente, Oakland, CA, USA. dustin.g.mark@kp.org
authors.forename: Dustin G
authors.initials: DG
authors.lastname: Mark
authors.forename: Yun-Yi
authors.initials: YY
authors.lastname: Hung
authors.forename: Steven R
authors.initials: SR
authors.lastname: Offerman
authors.forename: Adina S
authors.initials: AS
authors.lastname: Rauchwerger
authors.forename: Mary E
authors.initials: ME
authors.lastname: Reed
authors.forename: Uli
authors.initials: U
authors.lastname: Chettipally
authors.forename: David R
authors.initials: DR
authors.lastname: Vinson
authors.forename: Dustin W
authors.initials: DW
authors.lastname: Ballard
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001499:Bayes Theorem; D001774:Blood Chemical Analysis; D016022:Case-Control Studies; D002423:Cause of Death; D016001:Confidence Intervals; D004502:Education, Medical, Continuing; D004636:Emergency Service, Hospital; D005188:False Negative Reactions; D005260:Female; D005500:Follow-Up Studies; D015600:Glasgow Coma Scale; D006801:Humans; D008297:Male; D008875:Middle Aged; D010808:Physical Examination / Q000379:methods; D011237:Predictive Value of Tests; D018570:Risk Assessment; D013129:Spinal Puncture / Q000379:methods; D013345:Subarachnoid Hemorrhage / Q000134:cerebrospinal fluid / Q000000981:diagnostic imaging* / Q000401:mortality*; D015996:Survival Rate; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult