See also

Meningitis and encephalitis
Meningococcal disease
Lumbar puncture
Antimicrobial guidelines 

This guideline aims to help with the interpretation of CSF results for the purpose of diagnosing or excluding meningitis. The use of CSF for other purposes (including the diagnosis of specific neurological conditions, subarachnoid haemorrhage or malignancy) is outside its scope.      

Key Points

1. Normal CSF parameters vary with age
2. The presence of any neutrophils in the CSF is unusual in normal children and should raise concern about bacterial meningitis
3. In the case of a traumatic tap, rules based on a predicted white cell count in the CSF are not reliable
4. If the CSF is abnormal the safest course is to treat as if it is bacterial meningitis
   

Normal values

* Some studies have found that up to 5% of white cells in neonates without meningitis comprise neutrophils

Meningitis can occur in children with normal CSF microscopy. 

If there is a high clinical suspicion of meningitis, children who have a normal CSF should still be treated with IV antibiotics, pending cultures. 

CSF white cell count and protein level are higher at birth and fall fairly rapidly in the first 2 weeks of life.       

Interpretation of abnormal results

• Gram stain may be negative in up to 60% of cases of bacterial meningitis, even without prior antibiotics
• A predominance of lymphocytes does not exclude bacterial meningitis
• Neutrophils may predominate in viral meningitis, even after the first 24 hours
• If the CSF is abnormal, the safest course is to treat for bacterial meningitis
  

Other factors affecting results

Antibiotics prior to lumbar puncture

• Antibiotics are unlikely to significantly affect the CSF cell count or biochemistry in samples taken <24 hours after administration 
• Prior antibiotics usually prevent the culture of bacteria from the CSF

Seizures

• Seizures do not cause an increased CSF cell count

Traumatic (blood stained) tap

• The safest interpretation of a traumatic tap is to count the total number of white cells, and disregard the red cell count. If there are more white cells than the normal range for age, then the safest option is to treat
• Some guidelines suggest that in traumatic taps, the white blood cell and protein count can be corrected based on the following calculation: 1 white blood cell for every 500–700 red blood cells and 0.01 g/L protein for every 1000 red cells. However, this is unreliable
• Consider subarachnoid hemorrhage when there is unexplained or persistent RBCs in CSF
  

Time between sampling and analysis

• Delays in laboratory analysis of CSF can alter the cell count as a result of lysis in the CSF. There is progressive reduction in both neutrophils and lymphocytes after 4 hours

Additional tests

PCR

• PCR is routinely available for Neisseria meningitidis, Streptococcus pneumoniae, Herpes simplex virus (HSV), Enterovirus and Parechovirus 
• As results are not immediately available, they only help with decisions concerning discontinuing treatment
• Meningococcal PCR is particularly useful in patients with a clinical picture consistent with meningococcal meningitis, but who have received prior antibiotics
• HSV PCR should be requested for patients with clinical features of encephalitis.  It may be falsely negative in the first 36–72 hours of the illness. Consider repeating lumbar puncture and CSF PCR after this time if there is a high index of suspicion
• Consider requesting Enterovirus and Parechovirus PCR on CSF from patients with clinical and/or CSF features of viral meningitis

Bacterial antigens

• CSF bacterial antigen tests have low sensitivity and specificity
• They should therefore never influence treatment decisions and have little role if any in current management
  
  

Last Updated August 2019