Clinical use
Investigation of cerebrospinal fluid (CSF) samples for bacterial and fungal infection.
Background
To aid in the diagnosis of meningitis, encephalitis and other CNS infections laboratory examination of the CSF is required. CSF is usually obtained by lumbar puncture when there are no contraindications to this procedure, although ventricular, cisternal or fontanelle taps may also be used.
Acute meningitis, encephalitis, poliomyelitis and suspected meningococcal disease are all notifiable diseases, and clinically suspected cases should be notified to the local Health Protection team by the treating clinician.
In cases of aseptic meningitis, HIV testing should be offered to the patient.
The laboratory examination of CSF includes:
- White Blood Cell (WBC) and Red Blood Cell (RBC) counts
- WBC differential (lymphocytes vs. polymorphs)
- Examination of Gram-stained smear
- Culture
- Determination of glucose and protein concentrations (performed by clinical biochemistry departments)
- PCR (on request only)
In cases of suspected meningococcal disease in addition to CSF the following samples should be sent:
- Blood cultures
- Throat swab for bacterial culture (noting on request form ?Meningococcal disease)
- EDTA blood for meningococcal PCR
Intra-cerebral or sub-arachnoid haemorrhage or a traumatic spinal tap can result in the presence of RBC. Several sequential samples from one lumbar puncture are examined. Uniform blood staining of all samples suggests previous haemorrhage, whereas reducing counts in later obtained samples suggest bleeding induced by the tap procedure.
Reference ranges
For CSF cell counts:
WBC
| Age range | Age | Range |
|---|---|---|
| Neonates | less than 28 days | 0-30 cells x 106/L |
| Infants | 1 to 12 months | 0-15 cells x 106/L |
| Children/Adults | 1 year + | 0-5 cells x 106/L |
RBC
No RBCs should be present in normal CSF
Glucose
| Age range | Age | Range |
|---|---|---|
| Neonates | less than 28 days | 1.94-5.55 mmol/L |
| Infants | 29 to 58 days 2 to 12 months | 1.55-5.55 mmol/L 1.94-5.0 mmol/L |
| Children/Adults | 1 year + | 2.22-4.44 mmol/L |
Proteins
| Age range | Age | Range |
|---|---|---|
| Neonates | less than 28 days | 0.65-1.5 g/L |
| Infants | 29 to 56 days | 0.5-0.9 g/L |
| Children | 2 months to 18 years | 0.05-0.6 g/L |
| Adults | 18 to 60 over 60 | 0.15-0.6 g/L 0.15-0.45 g/L |
Patient preparation
CSF should be collected sequentially into 3 or more separate containers together with a fluoride sample for glucose estimation. Each container must be numbered indicating the order of collection.
The first and the third specimens are used for microbiological examination and the second specimen for biochemical analysis. Aseptic technique should be employed.
Specimen requirements
- White top sterile universal
- Specimens 1 and 3 should be sent urgently to microbiology, within 2 hours of the sample being collected
- Do not refrigerate the sample before sending to the laboratory
Minimum volume
1-2 ml
Limitations and restrictions
The cell counts for CSF samples may be inaccurate if there is a delay in sending samples, this is because cells will disintegrate in the sample over time. Microscopy should be performed within 2 hours of the sample collection time to ensure the accuracy of the result.
Samples containing blood clots will not have a cell count performed or reported. Clotted samples will only be investigated with a Gram’s stain and culture.
Turnaround time
- Microscopy: 2 hours
- Culture: 49 hours
Analysing laboratory
Microbiology Lab, James Cook University Hospital, Marton Road, TS4 3BW
Additional information
The microbiology laboratory must be contacted by telephone to inform them of the subsequent arrival of a CSF sample. The requested should provide the laboratory with:
- Patient name
- Hospital number
- Date of birth
- Tests required
- Requestors name and role
- Contact number for the microscopy result to be telephoned back to
CSF samples are not routinely testing for fungal pathogens. If fungal investigation is required, please contact the Consultant Microbiologist to discuss this prior to sending samples to the lab.
Additional tests may be requested for Mycobacterium sp. ,bacterial PCR and other pathogens depending on the clinical risk factors of the case (travel, immunosuppression, occupational exposure), please discuss with the Consultant Microbiologist if required. These tests should be requested on a separate request form and a separate sample provided where possible.
Routinely only sample 3 will have a cell count performed. If sub-arachnoid haemorrhage (SAH) is suspected, this must be stated on the form to allow for both samples 1 and 3 to have a cell count performed to aid diagnosis.