Operating Principles B-5
B.2.3 Five-Part WBC Differential Method
Five-part WBC differential results are determined using two separate dilutions, and two counting ses-
sions. The first session is used to count EOS, while the second is the three-part differential and RBC
counting described above. In three-part only measurements, the EOS counting is omitted.
To determine EOS, EOS% and BAS, BAS%, a second sample preparation and counting is required.
25
µ
l of whole blood sample is diluted with a species-dependent volume of
Lyse 2
solution, a hemo-
lytic reagent and Diluent, to form a 1:200 dilution. During the incubation time, white blood cells will be
differentially hemolysed, so that eosinophils will retain a higher cellular volume.
After counting and sizing the cells, the software will
interpret all cells above the discriminator as eosinophils.
The user can observe the distribution of the cells on the
EOS histogram.
The number and percentage of BAS cells will be calcu-
lated using EOS and other internal parameters using a
mathematical formula.
The EOS count is then followed with a three-part differential count (described above) to provide the
rest of the WBC count, the RBC and the PLT and related parameters.
EOS
Histogram
EM1
78.8 fl
400 fl
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