CSF interpretation

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  • See also

    Meningitis - Encephalitis
    Meningococcal disease
    Lumbar Puncture
    Antibiotics

    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

      White cell count Biochemistry
    Age

    Neutrophils

    (x 106 /L)

    Lymphocytes

    (x 106/L)

    Protein

    (g/L)

    Glucose

    CSF : blood ratio (total)

      <1 month 0*   < 22 <1.0  

    ≥ 0.6

    (or ≥ 2.0 mmol/L)

     >1 month 0   ≤ 5 < 0.4  

    ≥ 0.6

    (or ≥ 2.5 mmol/L)

    * 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

      White cell count Biochemistry

    Neutrophils

    (x 106 /L)

    Lymphocytes

    (x 106/L)

    Protein

    (g/L)

    Glucose

    (CSF : blood ratio)

    Bacterial meningitis

    100-10,000

    (but may be normal)

    Usually < 100

    > 1.0

    (but may be normal)

    < 0.4

    (but may be normal)

    Viral meningitis Usually <100  

    10-1000

    (but may be normal)

    0.4-1

    (but may be normal)

    Usually normal
    TB meningitis Usually <100

    50-1000

    (but may be normal)

    1-5

    (but may be normal)

    < 0.3

    (but 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 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 0.01g/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

  • Reference List

    1. Connell, Tom, and Nigel Curtis. "How to interpret a CSF—the art and the science." Hot Topics in Infection and Immunity in Children II. Springer, Boston, MA, 2005. 199-216.
    2. Kestenbaum, Lori A., et al. "Defining cerebrospinal fluid white blood cell count reference values in neonates and young infants." Pediatrics 125.2 (2010): 257-264.
    3. Lyons, Todd W., et al. "Correction of Cerebrospinal Fluid Protein in Infants With Traumatic Lumbar Punctures." The Pediatric infectious disease journal 36.10 (2017): 1006.
    4. Shah, Samir S., et al. "Age‐specific reference values for cerebrospinal fluid protein concentration in neonates and young infants." Journal of hospital medicine 6.1 (2011): 22-27.
    5. Thomson, Joanna, et al. "Cerebrospinal fluid reference values for young infants undergoing lumbar puncture." Pediatrics 141.3 (2018): e20173405.