Beckman Coulter COULTER LH 750 System, Reference

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PN 4277248DD
3-1
3 3
OPERATION PRINCIPLES
3.1 COULTER METHOD
CBC Analysis
The Coulter method counts and sizes cells by detecting and measuring changes in electrical
resistance when a particle (such as a cell) in a conductive liquid goes 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
two submerged electrodes, one located on each side of the aperture. This causes an electrical
pulse that can be counted and sized.
While the number of pulses indicates particle count, the size of the electrical pulse is
proportional to the cell volume.
35,36,37,38
Differential Analysis
WBC differential analysis and classification occurs in the flow cell, where:
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.
DETAIL OF
APERTURE
INTERNAL
ELECTRODE
APERTURE
TUBE
SAMPLE
BEAKER
APERTURE
EXTERNAL
ELECTRODE
APERTURE
CURRENT
VACUUM
BLOOD
CELL
SUSPENSION