Cerebrospinal fluid (CSF) test

Cerebrospinal fluid (CSF) test

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Cerebrospinal fluid (CSF) test

Diagnosis of the bacteria or fungal meningitis by microscopic examination and culture with identification and susceptibility test of the isolated organism.

Types of specimen: CSF

Criteria of specimen rejection

Non sterile container 

Infection of C.S.F

CSF is a sterile fluid and does not contain any commensals, however, care should be taken not to contaminate the specimen with skin normal flora during collection

Common bacterial pathogen

  • Haemophilus influenzae
  • Neisseria meningitis
  • Streptococcus pneumoniae
  • Group A and B streptococci
  • Gram negative bacilli
  • Listeria monocytogenes
  • Treponema pallidum (rare)
  • Brucella (rare)
  • Salmonella (rare)
  • Toxoplsma (rare)

Microbes that cause chronic meningitis

  • M. tuberculosis
  • Cryptococcus neoformans
  • Coccidoides immitis
  • Histoplasma capsulatum
  • Blastomyces dermatitides
  • Candida spp.
  • Nocardia
  • Actinomyces

Quantity of specimen: 3 ml of CSF is sufficient for culture

Time relapse before processing the sample: CSF is an emergency specimen and should be processed immediately

Storage: Room Temperature

Specimen processing


  • 2 Blood Agar
  • Chocolate Agar
  • MacConkey Agar
  • Fluid Thioglycollate

Culturing procedure: As a general rule in CSF and body fluid specimens for culture, centrifuge clear specimen and inoculate plates and do staining from sediments. While turbid specimens may not be centrifuged.

Post specimen processing

Interfering factors

  • Patient on antibiotic therapy.
  • Improper sample collection.

Result reporting: Results of the microscopy and all positive cultures of CSF are reported immediately to the treating physician. Negative bacterial results are sent out 72 hours after the CSF is received.

Turnaround time: Gram stain result is reported within 30 minutes of specimen receipt

  • Positive Culture results = 3- 5 days
  • Negative Culture results = 2-3 days

Additional information

Several antigen detection methods are available for the direct detection of the polysaccharide capsular antigen of H. influenzae, N. meningitidis, S. pneumoniae and Group B streptococci in CSF which showed specificity and sensitivity of about 90-97%. Direct detection of Cryptococcus antigen in CSF is also available which replaced India ink in many laboratories. The routine culture for CSF does not include all organisms mentioned in the above

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