Cerebral Spinal Fluid (CSF) cell count, microscopy & culture (meningitis encephalitis)

Microbiology

Notes

• The information given here is intended for use by healthcare professionals. Please see Lab Tests Online-UK for more general advice, links and background.
• Analysis of CSF may be useful in the diagnosis of meningitis, encephalitis or sub-arachnoid haemaorrage
• Please inform the laboratory when these samples are collecte
• Investigations for protein, glucose and xanthochromia are performed in Chemical Pathology
• Investigations for viruses, Mycobacteria and other unusual organisms are referred to external laboratories
• If prion disease is suspected, before sending any samples, please contact the referral laboratory to agree the patient meets the testing criteria CJD (ed.ac.uk). When testing is agreed contact the Microbiology laboratory to advise.
• Meningitis and acute encephalitis are notifiable diseases. Click for Notification Form.

See also:

• Meningo-encephalitis viral PCR screen
  
• Meningococcal PCR
  
• Pneumococcal PCR
  
• Mycobacterium and TB PCR
  
• Cerebral Spinal Fluids (CSF) Protein and Glucose
  

Meningitis

(source: UK SMI Investigation of Cerebrospinal Fluid)

Therapy should not be delayed pending CSF microscopy or culture. It is important to initiate effective antimicrobial therapy quickly, and this may commence before the examination of the CSF.

CSF results will be uploaded and available through the Sunrise EPR results system.

The duty Consultant Microbiologist will contact the requestor to discuss significant results.

Clinical expectation is that infections of the central nervous system should be managed clinically and that no single result should be used in isolation to demonstrate the presence, or absence, of infection. Clinicians are encouraged to review all results on each sample, including biochemistry protein and glucose values, and to use all these results in the context of the patient under their care. Please discuss with the duty Clinical Microbiologist if any concern

The diagnosis of meningitis from the examination of CSF involves the following:

• Complete cell count
• Differential leucocyte count
• Examination of Gram stained smear
• Culture
• Determination of glucose and protein concentrations (Biochemistry)
• PCR where appropriate
• Antigen testing

Sub-arachnoid haemorrhage

(source: UK SMI Investigation of Cerebrospinal Fluid)

• The presence of RBCs in CSF can result from an intra-cerebral or sub-arachnoid haemorrhage or from a traumatic lumbar puncture in which peripheral blood contaminates the CSF. The presence of this contaminating blood may make interpretation of the CSF analysis more difficult, but rarely obscures CSF abnormalities associated with bacterial meningitis.
  
• Sequential samples 1 and 3, from one lumbar puncture, are examined. Uniform bloodstaining of all samples suggests previous haemorrhage into the sub-arachnoid space, whereas reducing counts in sequentially obtained samples suggest bleeding induced by the tap procedure.
  
• A WBC: RBC ratio of 1:500 to 1:1000 is generally regarded as not indicative of infection.
  
• CSF obtained more than 12 hours post intra-cranial haemorrhage may show raised WBC counts of up to 500 x 106/L as a result of an inflammatory response.
  
• Cell counts are not possible on clotted samples.
  

CJD

• Please call the Laboratory or Consultant Medical Microbiologist prior to sending a CSF for CJD testing.

Sample requirements

30mL sterile Universal

Ideally a minimum volume of 1mL is required for microscopy and culture. If other investigations are to be included a larger volume is desirable. For Mycobacterium investigations collect as much as possible. Optimal volume for adults is at least 6 mLs.

Please inform the laboratory when these samples are collected.

CSF is normally collected sequentially into three or more separate containers which should be numbered consecutively. Send samples 1 and 3 to Microbiology and sample 2 to Chemical Pathology.

Fluoride tubes for glucose estimation must be filled last because they may contain environmental bacteria which might otherwise contaminate samples for culture.

Required information

• Relevant clinical details
  
• Current or recent antibiotic therapy
  
• Travel history
  
• Immunocompromise
  
• Neurosurgery
  
• Intracranial prosthetic material e.g. CSF shunt
  

Storage/transport

Samples must be transported to the laboratory with minimal delay. A delay of more than 2 hours between sample collection and processing may affect the cell count.

Hold samples at room temperature if transport is delayed.

Turnaround time

Routine microscopy results within 1 hour of receipt. Specialist microscopy tests will take longer.

Routine cultures 2 days

Specialist investigations will take longer

Reference ranges

Normal CSF values (source: UK SMI Investigation of Cerebrospinal Fluid)

If RBCs are visible in normal CSF, this could be due to a traumatic lumbar puncture (LP) in which peripheral blood has contaminated the CSF.