Cerebrospinal fluid (CSF)

Microbiology

Notes

Modified Fuchs Rosenthal counting chamber

Meningitis

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
  • PCR where appropriate

Sub-arachnoid haemorrhage

(source: UK Standards for Microbiological Investigation - 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.

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.

30 mL sterile Universal

Required information

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

Storage/transport

Samples should be transported to the laboratory with minimal delay.  Refrigerate samples 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 Standards for Microbiological Investigation - Investigation of Cerebrospinal Fluid)

Leucocytes Neonates 0-30 cells x 10^6/L
  1-4 years old 0-20 cells x 10^6/L
  5 years - puberty 0-10 cells x 10^6/L
  Adult 0-5 cells x 10^6/L
Erythrocytes Newborn 0-675 cells x 10^6/L
  Adult 0-10 cells x 10^6/L
Protein     
Glucose    

Page last reviewed: 13/09/2017