Table 6

Typical cerebrospinal fluid findings in central nervous system infections

	Viral meningo-encephalitis	Acute bacterial meningitis	Tuberculous meningitis	Fungal	Normal
Normal CSF opening pressure is generally <20 cm for adults, <10 cm for children below age 8, but may be as high as 25 cm (Whiteley et al, Neurology* 2006;67:1690–1).
†A bloody tap will falsely elevate the CSF white cell count and protein. To correct for a bloody tap, subtract 1 white cell for every 700 red blood cells/mm³ in the CSF, and 0.1 g/dl of protein for every 1000 red blood cells.
‡A normal glucose ratio is usually quoted as 66%, though only values below 50% are likely to be significant.
Some important exceptions:
• In viral CNS infections, an early lumbar puncture may give predominantly neutrophils, or there may be no cells in early or late lumbar punctures.
• In patients with acute bacterial meningitis that has been partially pre-treated with antibiotics (or patients <1 year old) the CSF cell count may not be very high and may be mostly lymphocytic.
• Tuberculous meningitis may have predominant CSF polymorphs early on.
• Listeria can give a similar CSF picture to tuberculous meningitis, but the history is shorter.
• CSF findings in bacterial abscesses range from near normal to purulent, depending on location of the abscess, and whether there is associated meningitis, or rupture.
• A cryptococcal antigen test and India ink stain should be performed on the CSF of all patients in whom cryptococcus is possible.
Opening pressure	Normal/high	High	High	High–very high	10–20 cm*
Colour	“Gin” clear	Cloudy	Cloudy/yellow	Clear/cloudy	Clear
Cells/mm³	Slightly increased	High–very high	Slightly increased	Normal–high
	5–1000	100–50000	25–500	0–1000	<5†
Differential	Lymphocytes	Neutrophils	Lymphocytes	Lymphocytes	Lymphocytes
CSF/plasma glucose ratio	Normal	Low	Low–very low (<30%)	Normal–low	66%‡
Protein (g/l)	Normal–high	High	High–very high	Normal–high	<0.45†
	0.5–1	>1	1.0–5.0	0.2–5.0