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Cerebrospinal Fluid

Cerebrospinal fluid (CSF) is found in the subarachnoid space of the brain (within the ventricles) and spinal canal. It is produced by the choroid plexus in the ventricles of the brain and the cerebral vessels at the rate of 500ml/day. In an adult the average volume of CSF is about 150ml.

Actions of CSF

Most of these are theories:

  • Protection of the brain from trauma.
  • Transport of chemical mediators e.g. neuropeptides.
Indications
  1. Diagnostic lumbar puncture:
  2. Therapeutic lumbar puncture:
    • Benign intracranial hypertension.

CSF is usually obtained by lumbar puncture.
Also it is helpful to note appearance of CSF and the opening pressure (normal 10-20 cm H2O).

Analysis

Samples are usually sent for:

Biochemistry

  • Protein - high (> 0.4 g/L) levels seen in infection and infiltration disorders (falsely high results are seen if the sample is contaminated with blood).
  • Glucose - CSF glucose is usually 60 - 80% of plasma glucose. A blood sample for glucose should be taken at the same time as the lumbar puncture. Implies there is increased uptake of glucose in the CNS.

Microscopy, culture and sensitivity:

  • Cell count - white cells with differential (neutrophils and lymphocytes) and red cells. When performing a lumbar puncture red cells may be present as a result of damage to a blood vessel during the procedure (commonly called a “bloody tap”). To confirm whether this represents a subarachnoid haemorrhage the CSF is centrifuged: clear supernatant fluid confirms a bloody tap, where as the supernatant fluid is stained yellow in a subarachnoid haemorrhage (known as xanthochromic).
  • Gram stain - for bacterial organisms.

Additional investigations:

  • Xanthochromia - yellow appearance of CSF after centrifugation. This represents breakdown of haemoglobin. Seen in subarachnoid haemorrhage.
  • Oligoclonal bands - seen in multiple sclerosis and neurosyphillis.
  • Virology.
  • PCR (polymerase chain reaction) e.g. for tuberculosis, viral and partially treated bacterial meningitis.
  • Bacterial antigen testing - may be useful if PCR not available and patient partially treated.
  • India ink staining for cryptococcus.
  CSF Appearance CSF Protein CSF Glucose CSF Cell Count (per mm3) CSF Gram Stain Additional features
Normal Clear and colourless 0.2-0.4 g/l
(neonate <1.7 g/l)
60-80% of Plasma Glucose Low WCC
(up to about 20 in neonates and up to 5 in older children and adults)
No organisms Opening pressure
10-20 cm H2O
Bacterial Meningitis Cloudy and turbid (if severe) Raised >1.5 g/l Glucose level is <50% of the plasma level. Cell count is high (100 to 1000+) and mostly neutrophils. May see organisms e.g. gram negative diplococci in N. meningitidis. Opening pressure
high
Viral / Aseptic Meningitis Clear Raised or high end of normal Glucose level is usually within normal limits.
May be reduced in some cases of mumps and herpes simplex
Cell count is high (100 to 1000+) and mostly lymphocytes. No organisms PCR or special stains
may help identify organism.
Tuberculous meningitis Clear or slightly cloudy
May have a cobweb appearance.
Raised >1.5 g/l
Protein is high (much higher than bacterial meningitis)
Glucose level is <50% of the plasma level. Cell count is high (100 to 1000+) and a mixed pleocytosis with mainly lymphocytes. Negative PCR may help identify TB quickly
Subarachnoid haemorrhage Blood stained
(although not always)
Raised or high end of normal Glucose level is usually low. High number of RBCs No organisms Uniformly blood stained ± xanthochromia
Guillain-Barre Syndrome Clear Markedly raised Glucose level is usually low. Low WCC
(up to about 20 in neonates and up to 5 in older children and adults)
No organisms  
Multiple sclerosis Clear Raised Glucose level is usually within normal limits Mild pleocytosis with mononuclear cells. No organisms Oligoclonal bands may be present on CSF protein electrophoresis
Neoplastic infiltration Clear Raised Low glucose Lymphocytosis No organisms Cytology may detect neoplastic cells
Acknowledgements EMIS is grateful to Dr Gurvinder Rull for writing this article. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2007.
DocID: 777
Document Version: 21
DocRef: bgp766
Last Updated: 4 Jun 2007
Review Date: 3 Jun 2009


















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PS - Health and Poverty

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See also MAKEPOVERTYHISTORY North East for details and links to campaigns against poverty.

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