Cerebrospinal Fluid Analysis – Part 3 – CSF Stain and Culture, CSF electrophoresis

Sample 

• The analysis is done on the CSF fluid.

Special Stains

1. The most common stain use is the Gram stain.
2. Gram stain gives a preliminary diagnosis.
3. Gram stain will differentiate;
   1. Bacterial meningitis with the presence of bacteria whether it is cocci or bacilli and as gram-positive or negative.
   2. Viral meningitis will be negative.
4. The most common causative agents are H.Influenzae in children and Neisseria and Streptococcus in adults.

Culture and Sensitivity

1. Culture can identify the organism and the most common organism found are:
   1. Bacteria.
   2. Fungi.
   3. T.Bacilli.
2. Culture needs 24 to 48 hours to get a result. This may take up to 72 hours to get sensitivity.

Identification of Tuberculous bacilli:

1. CSF and sputum smears are stained for the Acid-fast bacilli.
   1. These are red, rod-shaped bacteria.
2. The conventional culture of the T bacilli takes 4 to 6 weeks of incubation.
3. BACTEC  method is a culture technique in which the growth medium for the culture of M.tuberculosis has added a substrate labeled with radioactive carbon. (¹⁴C).
   1. This substrate is used by the bacteria and produces radioactive carbon dioxide (14CO₂), from the substrate.
   2. This ¹⁴CO2is detected and quantitated.
   3. This will give quick identification of mycobacteria.
4. The polymerase chain reaction (PCR) method is also developed.
   1. This allows the amplification of genomes which can be detected by the genetic DNA probe.
   2. Mycobacterium is detected in 36 to 48 hours.

CSF protein electrophoresis

1. Indication:
   1. Electrophoresis is done to find any abnormality of the proteins and immunoglobulins.
2. This is helpful to diagnose:
   1. Multiple sclerosis.
   2. Neurosyphilis.
   3. Autoimmune diseases.
3. In Myelosclerosis typical findings are:
   1. Increased total proteins and this is mainly gamma globulins.
   2. There is a discrete sharp band in the gamma region called the oligoclonal band.
4. The oligoclonal band may be seen in HIV.
5. Electrophoresis differentiates CSF from serum, where is there is an extra band of transferrin in CSF and not in the serum.

Table of various type of meningitis:

Disease	Pressure	Gross	Glucose mg/dL	Protein mg/dL	TLC  count/mL	Type of Cells
Normal	70-200	Clear(C.L)	45-85	10-45	0-8	MN
Bact.Meningitis	Increased	Turbid	0-25 mg/dL	50-500	1000-2000+	Polys
Tub.Meningitis	Increased	clear/cobweb	15-45	50-100	100-300	Lympho
Poliomyelitis	Increased	clear	normal	50-200	50-250	poly/lympho
Subarachnoid Hemorrhage	increased	bloody	normal	50-100	normal	RBCs

MN = Mononuclear cells.
TLC = Total leucocytic count.
Mening. = Meningitis.
Lympho = Lymphocytes.
Haem = Haemorrhage.

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