Medonic CA530, User Manual

Page: 28 / 108

Measuring Principles
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3.3 Counting Time RBC & WBC
The microprocessor system checks the counting time for the RBC and PLT
counting process. The counting time is defined as being the time needed for the
sample to be drawn from the start- to the stop detector in the metering unit. See
RBC,WBC and PLT Concentration Detection on page 25.
A counting time, which is 'HI', may be caused by a blockage in the aperture. In
such case, the system rinses the aperture (orifice) automatically. It is advisable to
check the counting time by using isotonic diluent as a new sample. (To save the
original blood sample).
The counting time limits on the RBC/PLT process are 10.5 and 17.5 seconds re-
spectively. Normal counting time is 13.5+/- 2 seconds. If the counting time is
outside the limits, the text “LO” or “HI” will be displayed.
The counting time can be displayed using the left/right arrow keys and is shown
as:
- RBC-Time=
- WBC-Time=
Note:
The 'Counting time' is not related to the actual result. Atmospheric pressure vari-
ations, protein built-up within the orifice (aperture) and other secondary effects
that might cause pressure changes will NOT influence the counted parameters
RBC, PLT and WBC.
3.4 WBC Differentials
Within the 3-part diff. technology a general problem is found how to define the
correct settings of the discriminators for the lymphocyte, MID sized cell (mainly
Monocytes) and Granulocytes areas. Many analyzers are using a fixed discrimina-
tor analogue where fixed thresholds are used to separate the 3 populations. The
3 part. diff. technology is based on the reaction of the lyzer reagent(s) to each spe-
cific cell type. Lymphocytes are more lyzed compared to the Granulocytes, result-
ing in 2 main populations whereof the Lymphocytes will be the smallest.
The main problem is related to the Granulocyte population. The cytoplasma sur-
rounding the cells is slowly dissolved in the surrounding plasma in whole blood.
This means that the Granulocyte population is slowly collapsing and finally inter-
feres with the Lymphocytes.
Refer to the figure below where the same sample is analyzed after approx. 4, or
more, hours. It is clearly seen that a fixed discriminator technology is unreliable
whenever analysing blood exposed to time, high temperature or other factors that
reduce the cytoplasma surrounding the Granulocytes.