COULTER HmX Hematology Analyzer, Справочное руководство

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PN 4237523A 3-1
3 3
OPERATION PRINCIPLES
3.1 GENERAL PRINCIPLES
CBC Analysis
The Coulter method accurately counts and sizes cells by detecting and measuring changes in
electrical resistance when a particle (such as a cell) in a conductive liquid passes through a
small aperture. See Figure 3.1.
Figure 3.1 Coulter Method of Counting and Sizing
Each cell suspended in a conductive liquid (diluent) acts as an insulator. As each cell goes
through the aperture, it momentarily increases the resistance of the electrical path between
the submerged electrodes on either side of the aperture. This causes a measurable electronic
pulse. For counting, the vacuum used to pull the diluted suspension of cells through the
aperture must be at a regulated volume.
The number of pulses correlates to the number of particles. The height of the electrical pulse
is proportional to the cell volume.
37, 38, 39, 40
Differential Analysis
As the sample, prepared for differential analysis, streams through the flow cell (Figure 3.2)
these three measurements occur simultaneously on each individual white cell to classify it:
r
Low-frequency current measures volume.
r
High-frequency current senses cellular internal content through measuring changes in
conductivity.
r
Light from the laser bouncing off the individual WBC cells characterizes cellular surface,
shape, and reflectivity.
Vacuum
Internal
electrode
Blood cell
suspension
Aperture
tube
Aperture
Sample
beaker
External
electrode
Aperture
current
Detail of
aperture