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
|<10||Count all 9 squares|
|10 - 100||Count 4 corner squares|
|>100||Dilute for nucleated cell count|
|Slightly hazy||1:10||30 µL ||270 µL|
|Hazy|| 1:20||30 µL||570 µL|
|Slightly cloudy || 1:100||30 µL||2970 µL|
|Cloudy ||1:200||30 µL||5970 µL|
CSF Cell Count Guidelines -- Diluted fluid
Make a smaller dilution
10 - 100
Count 4 corner squares
Make a larger dilution