Interpretation of results

Examine the CSF collected using a bright white light source for general appearance. It is best to hold the second tube against a white paper background so as to detect any subtle color changes. Normal CSF should be crystal clear and colourless.

Examine the CSF fluid for a blood-tinged appearance. Blood may be present for a number of reasons, including SAH. A "traumatic tap" occurs if the needle inadvertently has entered an epidural vein during insertion.

A yellowish tinge to the CSF fluid is called xanthochromia. Xanthochromia is usually caused by red blood cell degeneration in the CSF as would be seen in subarachnoid hemorrhage (SAH). The breakdown of red blood cells takes many hours to occur. Xanthochromia would be reliably seen by 12 hours and can persist for up to 2 weeks [this assumes that Vermulen¹ was correct. His paper is a case series of patients with known SAH, not undifferentiated headache patients. The detection of xanthochromia in this study employed spectrophotometry.] Other causes of xanthochromia include systemic jaundice and conditions causing elevated CSF protein.

¹ Vermeulen M, Hasan D, Blijenberg BG, Hijdra A, van Gijn J. Xanthochromia after subarachnoid haemorrhage needs no revisitation. J Neurology, Neurosurgery and Psychiatry 1989; 52:826-828.

It has been reported that detecting and quantifying xanthochromia may be more accurate using a spectrophotometer. Currently the availability of this testing method is limited in North America. The overall sensitivity and specificity of the technique are not currently known in the patient with an undifferentiated headache.

Use a standard laboratory reference to interpret the results of the CSF fluid analysis. Emergency physicians may need to seek consultation with an appropriate specialty service.

Normal	Erythrocytes: <10 X 10 6/L *Presence of more than a few RBCs may indicate cerebral or subarachnoid hemorrhage or traumatic tap.
Subarachnoid hemorrhage (SAH)	Xanthochromia may be present (see above in this section).Red cells are present after SAH and may be present after trauma, or with haemorrhagic inflammation (e.g. HSV encephalitis from Herpes Simplex Virus). If there is blood, determine if there is more blood in tube 1 than in tube 4. Typically RBC counts are comparatively higher in tube 1 than in tube 4 in a traumatic tap and roughly equal in SAH.
*Laboratory Information Handbook 2002, The Ottawa Hospital

In meningitis:
Turbidity or cloudiness can be seen when the white blood cell count (WBC) of the CSF is elevated. A high WBC indicates that there is inflammation of the central nervous system, as in meningitis for example.

	WBC in CSF	Glucose in CSF	Protein in CSF
Normal	Expected value Leukocytes (mononuclear): adult: 0-10 X 10 6/L* neonates: 0-30 X10 6/L*	Ref Interval: 2.7 -4.4 mmol/L (~0.6 _ serum conc)*	Ref Interval: 0.12-0.60 g/L Conversion factor: mg/L X 0.001 = g/L*
Bacterial meningitis	elevated predominantly neutrophils	May be low	May be high
Viral meningitis	elevatedpredominantly lymphocytes neutophils may be seen early	Usually normal
A traumatic tap may result in blood in the CSF. There should only be 1 white cell to every 700 red cells. A higher ratio indicates the possibility of meningitis. A brief course (less than 2 days) of antibiotic therapy is unlikely to affect the CSF cell count, protein or glucose levels but does reduce the probability of seeing bacteria with a Gram stain or of isolating an organism from cultures.In TB or fungal meningitis, mostly lymphocytes or monocytes are seen. Low CSF glucose levels, as compared to plasma levels, are seen in bacterial meningitis, cryptococcal meningitis, malignant involvement of the meninges and sarcoidosis. High CSF protein levels are seen: in conditions in which there is pus or blood in the CSF, with meningeal inflammation (e.g. purulent or tuberculous meningitis),with increased blood-brain vascular permeability (e.g. encephalitis, Guillain-Barré syndrome), with local immunoglobulin production (e.g. multiple sclerosis), where CSF circulation is impeded (e.g. spinal tumour).
*Laboratory Information Handbook, The Ottawa Hospital