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The page below is a sample from the LabCE course Cerebrospinal Fluid. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Cell Counting Guidelines

If cells are numerous and overlapping and it is necessary to focus through several planes in order to see all of the cells, a dilution must be made. When macroscopic appearance is turbid or milky, a significant dilution is usually necessary. Calibrated automatic pipettes should be used for specimens that require a dilution. Mouth pipetting must of course always be avoided.
Automated cell counters may not be the best choice for cell counts on CSF because of the variation in background counts. A high background count could cause a false increase in normal or slightly elevated counts.
The dilution required is based on the appearance of the sample. Cloudy fluids should be briefly examined microscopically and the necessary dilutions approximated. The guidelines in the tables below may be helpful when determining the area of the hemocytometer to count and when to make a new dilution:

CSF Cell Count Guidelines -- Undiluted fluid
Nucleated Cells / Square
Area to Count on Both Chambers
<10Count all 9 squares
10 - 100Count 4 corner squares
>100Dilute for nucleated cell count

Suggested dilutions

AppearanceDilution RatioVolume of SampleVolume of Diluent
Slightly hazy
30 µL 270 µL
30 µL
570 µL
Slightly cloudy
30 µL
2970 µL
30 µL
5970 µL
CSF Cell Count Guidelines -- Diluted fluid
Nucleated Cells / Square
Area to Count on Both Chambers
Make a smaller dilution
10 - 100
Count 4 corner squares
Make a larger dilution