title: Time-dependent test characteristics of head computed tomography in patients suspected of nontraumatic subarachnoid hemorrhage.
abstract: OBJECTIVE
  A recent study suggested that in patients with acute headache suspicious of nontraumatic subarachnoid hemorrhage (SAH), cerebrospinal fluid (CSF) analysis is not needed to rule out SAH if head CT performed ≤6 hours after ictus is negative. Before implementation in daily practice, these results need replication. Therefore, we investigated test characteristics of head CT in patients with a clinical suspicion of SAH.
  
  
  METHODS
  Patients suspicious of SAH and a normal level of consciousness presenting to our tertiary care hospital between 2005 and 2012 were included. All patients had a head CT interpreted by experienced neuroradiologists and CSF spectrophotometry if head CT was negative or inconclusive. We determined test characteristics with 95% confidence intervals (CI) for nontraumatic SAH of head CT performed ≤6 or >6 hours after onset of headache.
  
  
  RESULTS
  Sensitivity of head CT ≤6 hours after ictus (n=137) was 98.5% (95% CI, 92.1%-100%), diagnosing all patients with aneurysmal and perimesencephalic SAH, but not with a cervical arteriovenous malformation. Sensitivity of head CT performed >6 hours after ictus (n=113) was 90.0% (95% CI, 76.3-97.2). After exclusion of patients with an atypical presentation without headache, sensitivity, specificity, negative predictive value, and positive predictive value of head CT ≤6 hours were all 100%.
  
  
  CONCLUSIONS
  In patients presenting with acute headache and a normal head CT ≤6 hours after ictus, as interpreted by experienced neuroradiologists, there is no added value of CSF analysis. In patients with an atypical presentation without headache and in patients presenting >6 hours after ictus, CSF analysis is still indicated.
authors: Department of Neurology and Neurosurgery, UMC Utrecht Stroke Center, Utrecht, The Netherlands.
authors: Daan
authors: D
authors: Backes
authors: Gabriel J E
authors: GJ
authors: Rinkel
authors: Hans
authors: H
authors: Kemperman
authors: Francisca H H
authors: FH
authors: Linn
authors: Mervyn D I
authors: MD
authors: Vergouwen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001663:Bilirubin / Q000134:cerebrospinal fluid; D015331:Cohort Studies; D016001:Confidence Intervals; D016208:Databases, Factual; D005260:Female; D015600:Glasgow Coma Scale; D006257:Head / Q000000981:diagnostic imaging*; D006261:Headache / Q000209:etiology; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D013056:Spectrophotometry, Ultraviolet; D013129:Spinal Puncture; D013345:Subarachnoid Hemorrhage / Q000000981:diagnostic imaging*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: D001663:Bilirubin