title: What is the role of cerebrospinal fluid ferritin in the diagnosis of subarachnoid haemorrhage in computed tomography-negative patients?
abstract: BACKGROUND
  Spectrophotometry of cerebrospinal fluid (CSF) for bilirubin is the recommended method for investigation in suspected cases of subarachnoid haemorrhage (SAH), when a computed tomography (CT) of the head is negative for blood. There is a potential need for a simpler alternative. Measurement of CSF ferritin might fulfil this need.
  
  
  METHODS
  We have measured ferritin in the CSF from 252 patients with suspected SAH who were negative on a CT of the head for blood, recruited on a consecutive intention to recruit basis from four centres. CSF spectrophotometry was performed on all samples. A positive outcome was taken as an aneurysm found on angiography that was treated or a discharge diagnosis of non-aneurysmal SAH.
  
  
  RESULTS
  A final diagnosis of aneurysmal SAH was made in six patients, an arteriovenous malformation in one and non-aneurysmal SAH in nine. Receiver operating characteristic (ROC) analysis showed that at 6.4 microg/L, sensitivity, specificity, positive and negative predictive values were 1.0, 0.48, 0.12 and 1.0, respectively. At 12 microg/L, these values were 0.81, 0.91, 0.38 and 0.98, respectively.
  
  
  CONCLUSIONS
  At an appropriate negative predictive value (1.0) for a rule-out test, ferritin has too low a specificity to function as a stand-alone test and we cannot recommend it as an initial screen to be followed by spectrophotometry.
authors.affiliation: Department of Neurobiochemistry, The Walton Centre for Neurology and Neurosurgery, Liverpool L9 7LJ, UK.
authors.forename: Ian D
authors.initials: ID
authors.lastname: Watson
authors.forename: Robert
authors.initials: R
authors.lastname: Beetham
authors.forename: Michael N
authors.initials: MN
authors.lastname: Fahie-Wilson
authors.forename: Ian B
authors.initials: IB
authors.lastname: Holbrook
authors.forename: Daniel M
authors.initials: DM
authors.lastname: O'Connell
mesh_terms: D005293:Ferritins / Q000134:cerebrospinal fluid*; D006801:Humans; D013345:Subarachnoid Hemorrhage / Q000175:diagnosis* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed
chemical_list: D005293:Ferritins