Measuring Principles
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3.5 MCV (Mean Cell Volume RBCs)
The MCV parameter is derived from the RBC distribution curve. As the distribu-
tion curve has a maximum volume range of 250fl, the maximum channel also
contains clumps of cells that are larger than this volume. Therefore this channel
is excluded from the MCV calculation. The MCV is calculated from the volume
position of the discriminator to 249 fl. Be aware that the discriminator might be
“floating” or fixed by the user in menu 5.6.x.
In general, RBC counts that are lower than 0.60 (displayed value) do not give a
MCV/HCT value due to low statistical significance.
If the MCV is calibrated by using the “Calibration” program, found in the “Set-
up” menu; the whole curve is recalculated and moved in a correct way that re-
flects the new calibration setting. The printed curve will therefore always be cor-
rect in respect to the actual MCV value.
3.6 RDW% (Red Cell Distribution Width)
The RDW% parameter is calculated from the RBC distribution curve. The CV of
the curve is calculated. However, the CV is only calculated on a portion of the
curve. This avoids that other populations might interfere. The RDW% value is
therefore only measured on a portion of the RBC size distribution curve. I.e. not
all particles are included in the RDW% calculation.
The RDW% parameter is only valid if the MCV value is not zero.
3.7 RDWa (Red Cell Distribution Width
Absolute)
The RDWa parameter (absolute) is calculated from the RBC distribution curve at
a fixed level. In contrast to the RDW% parameter, which is expressed in CV, the
RDWa parameter measures the absolute width of the curve. The RDWa parame-
ter is only displayed if the MCV value is not zero. The RDWa parameter is for
investigational purposes only. No “normal” ranges are given.
3.8 HCT (Hematocrit)
The HCT is defined as being the packed volume of red cells in whole blood and
is calculated through MCV * RBC.
If no MCV is derived from a sample due to too low a number of RBC cells, no
HCT is calculated.
3.9 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 discrim-
inator is done in the set-up menu 5.6.
The platelets are determined from the same dilution as the RBC, in fact, the sys-
tem is counting just “cells” during the RBC/PLT counting process. The determi-
nation 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 behaviour
(floating or fixed).
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