Protein This is usually increased in infection, and also in some other CNS disorders. Highest in TB, then bacterial infections, then viral. Other CNS causes of elevation can generally be considered as inflammatory processes: GBS, sarcoidosis, vasculitis, CNS blood
Glucose There are absolute values for this but it is usually a ratio of serum levels. A ratio of 0.6 is normal. Infections (although less common in viral) lower this level, as can inflammatory processes (vasculitis, sarcoidosis).
WBC This refers to the cell count, which may be impacted by trauma from the sampling. There is normally on very few monocytes present. In the case of a ‘bloody tap’ a ratio of 1:500 WBC:RBC (or equivalent to the peripheral ratios) is taught, but may be misleading. Bacterial infections show a polymorphonuclear leukocytosis. Other infections (viral, TB, fungal) show more of a lymphocytosis. Seizures and GBS can also elevate the levels
Appearance The appearance should be clear and colourless. It may be frankly turbid in bacterial infection. In SAH it may be very bloody, but there can be some blood from traumatic sampling
Opening Pressure The normal opening pressure is 8-15 cmH20 (up to 20 is quoted in some links) Over 20 is high. It is important that this is measured in the lateral position.
Gram Stain/Culture This will be undertaken in cases of presumed bacterial infection to look for evidence of bacterial cells (and their characteristics). Culture of the CSF can then be undertaken.
Extended culture - listeria and cryptococcus
India ink stain - for cryptococcus
Viral PCR - enterovirus, HSV and others
ZN stain - for acid fast bacilli
Some pathologies have clear ‘phenotype’ of CSF.
Protein - high - >1
Glucose - low - < 2.2 (ratio <0.4)
WBC - high
Opening pressure can be elevated
The CSF can appear turbid
Protein - < 1
Glucose - normal (ratio >0.6)
WBC - high
Very high PMN count less common
Opening pressure may be normal or only mildly increased