Medonic M16C-US - Page 82

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10.5 Parameter Definitions (continued)
PLT (Platelets)
 Platelets are defined (for the purpose of discrimination) as cells in a range from
2.5fl to the discriminator level that is either set on a fixed volume or 'floating' and
determined by the software on each sample. The setting of the upper discriminator
is done in the setup menu.
 The platelets are determined from the same dilution as the RBC, in fact, the system
is counting just 'cells' during the RBC/PLT counting process. The determination of
which cell is a PLT or RBC is done at the end of the counting procedure and fully
determined by the setting of the user defined discriminator behavior (‘floating’ or
fixed)
 Example: 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
division factor 6.75.
 The reproducibility is directly dependent on the total number of cells entering the
orifice.
 Measuring PLT from the same dilution as RBC, the CV will be less than 3.5% for
most of the samples within normal range. A 'mean' CV of about 3.2 % is expected
for well-treated fresh EDTA whole blood samples within the range of 250-350
10e3/uL.
 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 well-balanced
mathematical correction algorithm for these effects within the software.
 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
affected. 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 a not
well-defined RBC-PLT population.
MPV (Mean
Platelet Volume)
 The mean cell volume of the platelets is determined from the PLT size distribution
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 can be programmed as 'floating' or fixed.
 MPV is not displayed in case of extreme low PLT counts due to high statistical
inaccuracy of such a population.
MCH (Mean Cell
Hemoglobin)
The MCH is a calculated value and is defined as HGB/RBC giving the mean HGB
concentration in the red cells.
MCHC (Mean
Cell Hemoglobin
Concentration)
 The MCHC is a calculated value and is defined as HGB/HCT.
 The MCHC is calculated from 3 measured parameters and therefore an excellent
instrument stability check. MCHC=HGB/HCT=HGB/(MCVxRBC).
 In general it could be stated that if a daily mean value is found outside the range
32-36 g/dl, the instrument has been incorrectly calibrated. The daily mean value of
the MCHC parameter should always be 34.5 +/- 1.5 g/dl.