CSF microbiology


Test indications

Investigation of suspected CNS infection or subarachnoid haemorrhage.

Test information

Microbiological investigations of CSF include:

  • Cell count
  • Gram and special stains (e.g. AFB)
  • antigen tests (as applicable)
  • culture
  • PCR (sent away - after discussion)
  • cryptococcal antigen (CRAG) (when requested)

Cell count will not be done on samples that are over 12 hours old. This is because cells disintegrate over time and extended delays may produce a cell count that does not reflect the clinical situation of the patient.

Note protein, glucose, xanthochromia scan and oligoclonal bands are done in Biochemistry.

Microscopy will normally be available within 4 hours of receipt of the sample in the laboratory. Only when infection is suspected will microscopy results be phoned to the clinician ordering the test.

Antigen tests and referral for PCR will be performed as appropriate.

All positive cultures are phoned.

For out of hours testing, please contact the on-call Biomedical scientist via switchboard once the sample has been taken and transport has been arranged.

Samples required

5 mL specimen split between 3 sterile universal containers (clearly label specimens with numbers for order collected).

Click here for details of CSF collection.

If extra investigations e.g. AFB culture, PCR, a larger volume will be needed. If special tests required please supply full details.

Turnaround time

2 working days for routine culture. For more complicated presentations turnaround time may be up to 10 days.

Quoted turnaround times are the time from receipt of specimen into the laboratory to 90% of reports leaving the laboratory. Stated times are based on normal working hours, Monday to Friday, excluding statutory bank and public holidays.