Central Spinal Fluid, CSF culture- Specimen collection, Transport, Processing, Cell Count

Introduction to Central Spinal Fluid (CSF) culture

The central spinal fluid (CSF) is collected for the diagnosis of various disorders. It is tested for red blood cells (RBS), white blood cells (WBC), protein, glucose, or microbiological presence.

Specimen collection for Central Spinal Fluid (CSF) culture

Central Spinal Fluid (CSF) (2-5ml) is collected aseptically in lumbar puncture between L3, L4, and L5 and is distributed in 3 tubes:

• Tube 1 = chemistry (glucose and protein count, immunology study) even if blood cells/bacteria introduced during spinal tap are present in tube 1, tests are not affected

• Tube 2 = culture

• Tube 3 = for cell count and differentiation (cytology) as they are likely to contain cells introduced during the collection process

Specimen Transport for Central Spinal Fluid (CSF) culture

Central Spinal Fluid (CSF) should never be refrigerated. If rapid processing is not possible, it should be incubated at 35°C or left at room temperature before specimen transportation.

The samples should not be frozen as H. influenza and Listeria monocytogenes are sensitive to cold. Also, lymphocytes might disintegrate. Streptococcus. pneumoniae may be detectable in CSF after an hour or longer.

* Neutrophils may be lysed and count may be decreased by 32% after 1 hour and 50% after 2 hours.

Specimen processing for Central Spinal Fluid (CSF)

If the volume of Central Spinal Fluid (CSF) is greater than 1 ml, they should be centrifuged at 1500g for 15 mins. If CSF is less than 1ml, the specimen should be gram stained and plated directly to BA and CA plates.

After centrifugation, the supernatant (0.5ml) is removed to a sterile tube. The remaining fluid (0.5ml) is used to suspend the sediment.

Sediment is mixed (vortexed) with remaining fluid by forcefully aspirating the sediment up and down into a sterile pipette several times so that microorganisms are adequately dispersed and have not adhered to the tube.

A drop of sediment is Gram-stained (smear is never spread) to observe microorganisms, RBC, and inflammatory cells. The supernatant can be used to test for the presence of Ag, rapid diagnostic tests, etc.

Cell count in Central Spinal Fluid (CSF)

The lymphocytes are counted in Central Spinal Fluid (CSF) in order to classify meningitis into one of 3 clinical types:

• Hazy, cloudy, turbid CSF indicates tumors and bacterial meningitis

• Hemorrhagic CSF fluid may be indicative of anthrax meningitis

• Pellicle formation in CSF might indicate excess protein