17
3.3
Aspiration
If you want to analyze a whole blood sample, present the sample to the analyzer directly, and
the analyzer will aspirate 10μL of the whole blood sample.
If you want to analyze a capillary blood sample under the pre-dilute mode, you should first
manually dilute the sample (20μL capillary sample needs to be diluted by 0.58 mL of diluent
to form a 1:30 dilution), and then present the pre-diluted sample to the analyzer, which will
aspirate 183uL of the sample.
3.4
Dilution
Usually in blood samples, the cells are too close to each other to be identified or counted. For this
reason, the diluent is used to separate the cells so that they draw through the aperture one at a time
as well as to create a conductive environment for cell counting. Moreover, red blood cells usually
outnumber white blood cells by 500-1000 times. Because red blood cells usually have no nucleus,
they are eliminated when the lyse breaks down their cell walls. For this reason, lyse need to be added
to the sample to eliminate the red cells before the WBC counting. The analyzer provides whole blood
mode and pre-dilute mode for the analysis of different sample types.
3.5
WBC Measurement
3.5.1 Measurement Principle:
WBC measurement principle
The WBCs are counted by the impedance method. The analyzer aspirates certain volume of
sample, dilutes it with certain volume of conductive solution, and delivers the dilution to the
metering unit. The metering unit has a little opening which is called "aperture". A pair of
electrodes is positioned on both sides of the aperture, and creates a constant-current supply.
As cells are poor conductors, when each particle in the diluted sample passes through the
aperture under the constant negative pressure, a transitory change in the direct-current
resistance between the electrodes is produced. The change in turn produces a measurable
electrical pulse which is proportional to the particle size. And when the particles pass the
aperture in succession, a series of pulses are produced between the electrodes. The number
of pulses generated indicates the number of particles passed through the aperture; and the
amplitude of each pulse is proportional to the volume of each particle.
Each pulse is amplified and compared to the internal reference voltage channel, which only
accepts the pulses of certain amplitude. All the collected pulses are thus classified based on
the reference voltage ranges of different channels, and the number of the pluses in the WBC
channel indicates the number of the WBC particles. The cell size distribution width is
represented by the number of particles falling in each channel.
To Next Page
Loading...
Need help?
General
