Medonic CA530, User Manual

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Measuring Principles
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Let us suppose that a sample contains 200 000 platelets/µl in whole blood. After
a dilution of 1:40 000 the sample contains 200 000 divided by 40 000 = 5 cells/
µl. So, each µl drawn through the aperture gives 5 pulses. As the counting volume
(the volume of the metering glass tube) is 270 µl, the total number of cells that
are analyzed will be 5*270=1350 cells.
In other words, the total number passing through the orifice when determining
the PLT is the value shown on the display screen without decimals multiplied by
the factor 6.75.
The reproducibility is directly dependent on the total number of cells entering the
orifice. In the instrument, measuring PLT from the same dilution as RBC, the CV
will be less than 3.5% for most of the samples within normal range. The CV will
be lower for most samples, but on some samples it might be slightly higher. A
'mean' CV of about 3.2% is expected for well-treated fresh EDTA whole blood
samples within the range of 200-350 10
3
/µl. As the system uses an orifice size of
80 µm diameter, coincidence losses will take place with extreme sample RBC/
PLT counts. The system has a software with a well-balanced mathematical cor-
rection algorithm to minimize these effects
Please note that if a floating discriminator is used and no well-defined minimum
is found between the RBC and PLTs, the reproducibility of mainly the PLT is af-
fected. To check the reproducibility of the low PLTs, it might be wise to put the
analyzer in a fixed discriminator mode to exclude any error introduced by an ill-
defined RBC-PLT population.
CA620-CellGuard PLT (Platelets)
In case the CA620-CellGuard is programmed and used for PLT concentrates, the
reproducibility is better than the stated CV figures above, as CV is a concentra-
tion dependent parameter.
Note:
In case high numbers of RBCs are present using the PLT concentrate mode, PLT
will show a flag “RP” (Red cells Present) to warn the operator that the PLT pa-
rameter may not be correctly analyzed.
3.10 MPV (Mean Platelet Volume)
The mean cell volume of the platelets is determined from the PLT size distribu-
tion curve.
The MPV is defined as being the mean value of the PLT size distribution curve
from the lower discriminator (2.5 fl) to the position of the upper discriminator
which might be programmed as floating or fixed as set in menu 5.6.x.
MPV is not displayed in case of extreme low PLT counts due to high statistical
inaccuracy of such a population.
3.11 PDW (Platelet distribution width)
The PDW parameter is calculated from the PLT distribution curve at a fixed level.
The calulation of the PDW parameter is analogue to the RDWa parameter for
RBC.
The PDW parameter is only valid if the MPV value is not zero. This parameter is
for investigatory purposes only. No ‘normal’ range is supplied.