title: Serum glucose adjusted cut-off values for normal cerebrospinal fluid/serum glucose ratio: implications for clinical practice.
abstract: BACKGROUND
  Calculation of the cerebrospinal fluid/serum glucose (CSF/SGlu) ratio is part of the routine CSF work-up, however, different cut-off values ranging from 0.3 to 0.5 have been suggested so far to distinguish physiological from pathological conditions. The objective of this study was to determine cut-off values for normal CSF/SGlu ratio dependent on serum glucose concentrations.
  
  
  METHODS
  We screened our database for paired CSF and serum samples, which have been collected by lumbar puncture, were processed within 1 h after withdrawal, showed cell count <15/3, erythrocyte count <1500/3 and normal CSF total protein resulting in 1036 sample pairs. Glucose concentrations in CSF and serum were measured by enzymatic spectrophotometry.
  
  
  RESULTS
  Median glucose concentration in CSF was approximately 60% of that in serum. CSF/SGlu ratios negatively correlated with serum glucose levels (R=-0.586, p<0.001) and cut-off values for normal CSF/SGlu ratio defined as the 5th percentile were 0.5 for patients with serum glucose concentrations <100 mg/dL, 0.4 for those with a glucose level of 100-149 mg/dL and 0.3 for serum glucose concentrations ≥150 mg/dL.
  
  
  CONCLUSIONS
  CSF/SGlu ratio inversely correlates with serum glucose concentrations in a non-linear manner. These findings suggest that cut-off values for normal CSF/SGlu ratio must be adjusted to serum glucose levels, probably explaining the considerably varying cut-offs that have been reported so far.
authors.forename: Harald
authors.initials: H
authors.lastname: Hegen
authors.forename: Michael
authors.initials: M
authors.lastname: Auer
authors.forename: Florian
authors.initials: F
authors.lastname: Deisenhammer
mesh_terms: D000328:Adult; D000368:Aged; D001786:Blood Glucose / Q000378:metabolism*; D002452:Cell Count; D002555:Cerebrospinal Fluid / Q000737:chemistry / Q000166:cytology; D005260:Female; D005947:Glucose / Q000134:cerebrospinal fluid*; D006801:Humans; D006943:Hyperglycemia / Q000097:blood / Q000134:cerebrospinal fluid; D008297:Male; D008875:Middle Aged; D009422:Nervous System Diseases / Q000097:blood / Q000134:cerebrospinal fluid / Q000175:diagnosis; D017711:Nonlinear Dynamics; D010818:Practice Patterns, Physicians'; D012016:Reference Values
chemical_list: D001786:Blood Glucose; D005947:Glucose