title: Specificity of elevated cerebrospinal fluid bilirubin in the investigation of subarachnoid haemorrhage.
abstract: BACKGROUND
  The spectrophotometric examination of cerebrospinal fluid for bilirubin is an established investigation in patients with suspected subarachnoid haemorrhage. This study assesses the diagnostic specificity of an elevated cerebrospinal fluid bilirubin and how this may be influenced by the presence of oxyhaemoglobin and the concentration of cerebrospinal fluid total protein.
  
  
  METHODS
  One thousand cerebrospinal fluid spectroscopy reports were reviewed. Electronic patient records were examined to determine the clinical outcome in patients with an elevated cerebrospinal fluid bilirubin.
  
  
  RESULTS
  Forty-four out of 1000 cerebrospinal fluid scans showed an increase in cerebrospinal fluid bilirubin unrelated to elevated serum bilirubin concentrations. This was associated with subarachnoid haemorrhage in 16 (36%) cases. Subarachnoid haemorrhage was confirmed in 5/17 (29%) patients positive for cerebrospinal fluid bilirubin alone and in 11/27 (41%) patients positive for both cerebrospinal fluid bilirubin and oxyhaemoglobin. At cerebrospinal fluid total protein concentrations <1 g/L, the specificity for subarachnoid haemorrhage improved: 4/9 (44%) vs. 1/8 (13%) with an increase in cerebrospinal fluid bilirubin alone; 6/10 (60%) vs. 5/17 (29%) in patients with increases in both bilirubin and oxyhaemoglobin.
  
  
  CONCLUSIONS
  While an increase in cerebrospinal fluid bilirubin may be considered consistent with subarachnoid haemorrhage, the likelihood that a subarachnoid haemorrhage has occurred is influenced by the presence of oxyhaemoglobin and the concentration of total protein in the cerebrospinal fluid.
authors.affiliation: Department of Clinical Biochemistry and Haematology, Western General Hospital, Edinburgh, UK helen.falconer@luht.scot.nhs.uk.
authors.forename: Helen L
authors.initials: HL
authors.lastname: Falconer
authors.affiliation: Department of Clinical Biochemistry and Haematology, Western General Hospital, Edinburgh, UK.
authors.forename: Susan A
authors.initials: SA
authors.lastname: Walker
authors.affiliation: Department of Clinical Biochemistry and Haematology, Western General Hospital, Edinburgh, UK.
authors.forename: J
authors.initials: J
authors.lastname: Peter Ashby
mesh_terms: D001663:Bilirubin / Q000134:cerebrospinal fluid*; D006801:Humans; D056951:Photoelectron Spectroscopy / Q000592:standards*; D013345:Subarachnoid Hemorrhage / Q000134:cerebrospinal fluid*
chemical_list: D001663:Bilirubin
keywords: Cerebrospinal fluid bilirubin; cerebrospinal fluid oxyhaemoglobin; cerebrospinal fluid total protein; subarachnoid haemorrhage