Abaxis VetScan HM5, Operator'S Manual

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Introduction to Veterinary Hematology A-5
A.3.2 White Blood Cells
White Blood Cells — WBC — are formed in the bone marrow. During their maturation sequence they
differentiate from the stem cells into mature sub-populations. WBCs are nucleated and classified as
granulocytes (neutrophils, eosinophils, and basophils), lymphocytes, and monocytes. WBCs are
equipped with all cell organelles necessary to perform vital protective functions in the body.
Normal WBC counts are a fraction of the RBC population. In pathological conditions, the WBC count
can increase dramatically (up to 300 x 10
9
cells/l in extreme leukemia). In these cases, predilution of
the sample is recommended for the most accurate results (see “Three-Part Differential Method” on
page B-3 ).
Three-part differential histograms (volume distribution curves) of WBCs can be used as a simple,
visual evaluation of the number and relative percentage of lymphocytes (LYM, LYM%), monocytes
(MON, MON%), and granulocytes (GRA, GRA%).
WBC-related parameters are defined as follows:
WBC = LYM + MON + GRA
LYM% = LYM / WBC
MON% = MON / WBC
GRA% = GRA / WBC
NEU% = (GRA – EOS – BAS) / WBC
EOS% = EOS / WBC
BAS% = BAS / WBC
Elevated WBC counts can affect other differential parameters. It is highly recommended that abnormal
WBC and other cell differentials be confirmed by a manual blood smear, as is the case with all auto-
mated hematology analyzers.
1
A.3.3 Automated WBC Classification
The analyzer evaluates each sample as a unique population, using dynamic cellular discriminators to
assess the cellular distribution most accurately. To determine WBC sub-populations, the analyzer first
sets “discriminator 1” at the limit of hemolysed RBCs + PLTs (on the left in the following graph) and
LYM population, then fits normal distribution curves to the remaining WBC histogram (shown below
in different shades of gray).
1. Bessman, JD. Automated Blood Counts and Differentials. A Practical Guide. (Baltimore: Johns Hopkins University Press, 1986),
p. 107.