See also

Meningitis and encephalitis
Meningococcal disease
Lumbar puncture
Antimicrobial guidelines

Key points

1. If CSF is abnormal, the safest option is to commence empiric antimicrobial treatment for bacterial meningitis
2. CSF parameters vary with age, which influences how a sample is interpreted
3. The presence of any neutrophils in the CSF, regardless of age, may indicate bacterial meningitis. Discussion with a senior clinician is recommended
4. In the case of a traumatic tap, interpret CSF results with caution. Do not rely on correcting the CSF white cell count for the number of red cells

Background

• Meningitis can occur in children with normal CSF microscopy
• If there is a high clinical suspicion of meningitis or encephalitis, children who have a normal CSF microscopy should still be treated with IV antimicrobials, pending cultures or PCR
• CSF white cell count and protein level are higher at birth and fall in the first 2 weeks of life       

Assessment

Normal values

Note: # Some studies have found that up to 5% of white blood cells in the CSF of neonates without meningitis, comprise neutrophils

Interpretation of abnormal results

Note: *may be normal

• 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 if the CSF sample was taken within 24 hours of antibiotic administration
• Prior antibiotics usually prevent the culture of bacteria from the CSF
• Partially treated meningitis (ie if the child has recently been on oral antibiotics) may result in a lower CSF neutrophil count than untreated bacterial meningitis

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 commence empiric antibiotics
• 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
• Consider subarachnoid haemorrhage when there are unexplained or persistently elevated red blood cells in CSF

Time between sampling and analysis

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

Additional tests

PCR

• CSF PCR is widely available for Neisseria meningitidis, Streptococcus pneumoniae, herpes simplex virus (HSV), enterovirus and parechovirus 
• Some health services have access to extended PCR panels (eg Biofire®) which test for multiple bacteria, viruses and fungi (Escherichia coli, Haemophilus influenzae, Listeria monocytogenes, N meningitidis, Group B Streptococcus, S pneumoniae, cytomegalovirus, enterovirus, HSV-1, HSV-2, human herpesvirus-6, parechovirus, varicella zoster virus, Cryptococcus neoformans, Cryptococcus gattii)
• Interpret with caution due to potential false positives, and correlate with CSF cell count
• Do not delay empiric treatment while waiting for PCR results
• 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 negative in the first 36-72 hours of the illness. Consider repeating lumbar puncture and HSV 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

Consider consultation with local paediatric team 

• All children with suspected encephalitis or bacterial meningitis
• All children with concern for non-infectious encephalopathy

Consider transfer when

• Haemodynamic or respiratory instability
• Altered conscious state, seizures or focal neurological signs
• Child requiring care above the level of comfort of the local hospital
• Complications of meningitis or encephalitis or poor response to treatment

For emergency advice and paediatric or neonatal ICU transfers, see Retrieval services

Parent information sheet

Lumbar puncture
Meningitis
Meningococcal infection

Last updated October 2024