10.4 Photometric Method – HGB Hemoglobin
HGB
(Hemoglobin
Concentration)
The hemoglobin is determined from the same dilution as the WBC. For each
sample a blank is measured as a reference, this means that any drift in reagent-,
cuvette-absorption, or diode is eliminated. The photometer system consists of a
photodiode, a cuvette with a length of 15 mm and a filter at a wavelength of 535
nm (bandwidth 20 nm). The HGB readings are slightly corrected for turbidity in
case of extreme WBC counts. The diode is switched off if the instrument is in
standby mode, giving it an extended lifetime.
Figure 10.4
10.5 Parameter Definitions
This section describes the parameter definitions that have not been defined yet in
other sections.
MCV ( Mean
Cell Volume
RBCs)
The MCV parameter is derived from the RBC distribution curve. As the
distribution 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 the 'Discriminator set-up program'
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' procedure, in the user manual,
the whole curve is recalculated and moved in a correct way that reflects the new
calibration setting. The printed curve will therefore always be correct in respect to
the actual MCV value.
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.
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.
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