What are the characteristic CSF findings in subarachnoid haemorrhage (SAH)? How can this be differentiated from a ‘traumatic tap’?

Normal
Traumatic Tap
Subarachnoid Haemorrhage
Opening Pressure (cm/H2O)
5-20
Normal
Elevated
Appearance
Clear, colourless
Grossly bloody or clear
Grossly bloody, xanthochromic or clear
RBC
(per mm3)
<3
Elevated
Typically varies from tube to tube (greatest in Tube #1)
Elevated
WCC
(per mm3)
<5
Elevated
(can correct by subtracting 1 per 1000 RBCs/mm3)
Elevated
(can correct by subtracting 1 per 1000 RBCs/mm3)
Protein
(g/L)
0.2-0.4
Elevated
(can correct by subtracting 10mg/L for every 1000 RBCs/mm3)
Elevated
(can correct by subtracting 10mg/L for every 1000 RBCs/mm3)
Glucose-Serum Ratio
0.5-0.66
(2.5-3.5 mmol/L)
Normal
Normal
Lactate
(mmol/L)
<2.8–3.5
Normal
Normal
Other
-
Xanthochromia absent
Xanthochromia typically present if duration over 2-12 hours