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4.2 Principles of Operation
The ‘ELite 5’ analyzer uses a combination of methods to provide measurement results:
• Volumetric impedance (the Impedance method) is used to determine the cellular
concentrations and volume distributions of leukocytes (WBC), erythrocytes (RBC),
and platelets (PLT).
• Photometric measurement of light absorbance is used to determine hemoglobin
(HGB) concentration.
• Optical measurement of light scattering and diffraction is used to determine 5-part
leukocyte (LYM%, MON%, NEU%, EOS%, BAS%) differential parameters.
4.2.1 Volumetric Impedance Method
The volumetric impedance method determines cellular concentrations and volume
distributions of cells by detecting and measuring changes in electrical impedance when
particles suspended in a conductive liquid pass through a small aperture. The method is
“volumetric” because a small known volume of blood is precisely diluted with a conductive
diluent and forced through the aperture at a fixed rate.
Figure 4. Volumetric Impedance Method
A constant direct current flows between the electrodes on either side of the aperture. Each cell
passing through the aperture causes a change in the electrical impedance of the conductive blood
cell suspension. This change is sensed by the ‘ELite 5’ electronics and converted to an electrical pulse.
The quantity of pulses is proportional to the number of particles. The intensity of each pulse is
proportional to the volume of the particle. The volume distribution diagrams of the particles result in
the WBC, RBC, and PLT histograms that measured in femtoliter volume units.
Electronic discrimination allows separation of erythrocytes (RBC) and platelets (PLT). A lytic
reaction lyses erythrocytes to clearly measure leukocytes (WBC).
4.2.2 Photometric Light Absorbance Method
A lysed blood sample dilution can be analyzed for hemoglobin (HGB) concentration based on
its stable chromogen content. The reagent lyses the red blood cells causing the release of
cellular hemoglobin. The hemoglobin concentration is measured by taking a photometric
reading across the ‘ELite 5’ WBC chamber. The HGB measurement is calculated as the
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