title: Should spectrophotometry be used to identify xanthochromia in the cerebrospinal fluid of alert patients suspected of having subarachnoid hemorrhage?
abstract: OBJECTIVE
  The absence of xanthochromia in the cerebrospinal fluid (CSF) is often used to exclude subarachnoid hemorrhage (SAH). Authorities advocate spectrophotometry to measure xanthochromia, but most North American hospitals use visual inspection. We studied the diagnostic accuracy of spectrophotometry for SAH, and its potential impact on current practice.
  
  
  METHODS
  This was a prospective cohort study comparing the diagnostic accuracy of tests. The study was set in 3 university-affiliated tertiary care emergency departments. We enrolled consecutive neurologically intact adults with nontraumatic headache undergoing lumbar puncture (LP) to rule out SAH. CSF was centrifuged, frozen and analyzed later in batch. SAH was defined by (1) subarachnoid blood on CT, (2) >5x10(6) red blood cells/L in the final CSF tube and positive angiography, or (3) visible xanthochromia in CSF and positive angiography. All subjects lacking a normal CT and LP were telephoned at 30 days.
  
  
  RESULTS
  We enrolled 220 patients (mean age 42+/-16 years; CT rate 87.7%; angiography rate 5.9%). Two SAHs were identified: 1 with red blood cells without xanthochromia in the CSF and 1 with visibly xanthochromic CSF. The specificity of xanthochromia was 97% (95% CI: 92% to 99%) for visual inspection, but as low as 29% (95% CI: 23% to 35%) for 2 of the spectrophotometric definitions. Introducing spectrophotometry could lead to angiography in as many as 11% to 71% of patients undergoing LP.
  
  
  CONCLUSIONS
  Spectrophotometric definitions of xanthochromia have only moderate to low specificity for SAH. Using spectrophotometry could increase angiography rates, thereby identifying more incidental aneurysms, increasing patient anxiety and exposing patients to unnecessary surgical or investigational complications without benefit.
authors.affiliation: Department of Emergency Medicine, University of Ottawa, ON, Canada. jperry@ohri.ca
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Perry
authors.forename: Marco L A
authors.initials: ML
authors.lastname: Sivilotti
authors.forename: Ian G
authors.initials: IG
authors.lastname: Stiell
authors.forename: George A
authors.initials: GA
authors.lastname: Wells
authors.forename: Jenny
authors.initials: J
authors.lastname: Raymond
authors.forename: Melodie
authors.initials: M
authors.lastname: Mortensen
authors.forename: Cheryl
authors.initials: C
authors.lastname: Symington
mesh_terms: D000328:Adult; D000368:Aged; D002533:Cerebral Angiography; D015331:Cohort Studies; D003116:Color; D003124:Colorimetry; D003243:Consciousness; D005189:False Positive Reactions; D005260:Female; D006261:Headache / Q000134:cerebrospinal fluid; D006801:Humans; D002532:Intracranial Aneurysm / Q000150:complications; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013053:Spectrophotometry; D013129:Spinal Puncture; D013345:Subarachnoid Hemorrhage / Q000134:cerebrospinal fluid* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed