Medonic CA530, Руководство пользователя

Страница: 27 / 108

Measuring Principles
1016en01 03-11-24 27
All cells smaller than the upper PLT discriminator level will not be recognised as
red cells. In case the user has selected a “floating” discriminator; RBC cells are
counted from the set-point of this variable discriminator, which varies from sam-
ple to sample between the volume limits set by the user.
The number of cells for determining RBC is counted from a suspension of
1:40 000 dilution ratio of whole blood.
Let us suppose that a sample contains 5 000 000 cells/µl. A dilution of 1:40 000
then give a final concentration of 5 000 000 divided by 40 000 = 125 cells/µl, so
each µl drawn through the aperture generates 125 pulses.
The measured volume drawn through the aperture is 270 µl (factory calibrated),
so the system will count 270*125 = 33 750 pulses. The analyzer uses a fixed divi-
sion factor of 67.5, so the display will show 33 750/67.5 = 500, which is the cor-
rect value.
With the size of the orifice and the concentration of cells, there will be a certain
coincidence in the orifice system. However this is a constant system factor and
compensated within the software by a correcting algorithm to make the RBC
count linear within the stated specifications.
Hence, the total number of cells passing through the aperture when determining
the RBC is the value on the display multiplied by the factor 67.5. Therefore, a
sample which gives 5.00 in the RBC display field has been analyzed by measuring
500 * 67.5 = 33 750 cells.
The reproducibility is directly related to the total number of cells entering the or-
ifice. The higher the concentration, the better the reproducibility. The instrument
has a dilution ratio for RBC of 1:40 000 and the CV will therefore be less than
1% for samples with an RBC number within the normal range.
3.2 Sizing RBC, WBC and PLT
The sizing is done in a matrix with the volume on the horizontal (x-) axis and the
number of cells on the vertical (y-) axis.
(The x-axis is divided into 2048 channels)
As stated above, a size distribution is performed for both PLT and RBC simulta-
neously. The 'RBC' distribution however, is the distribution with a higher volume
than the upper discriminator level which is marked on the display and printer as
a dotted vertical bar.
The maximum (RBC) cell size that can be analyzed is 250 fl. Clumps of cells larg-
er than this volume are analyzed as being 250 fl and are 'collected' in the highest
channel.
As the curves are 'normalised', the height of the distribution curve is not neces-
sarily related to the number of RBC cells counted.
The reproducibility of the curve is also dependent upon the concentration of cells
in the sample.
In cases with a low number of RBC cells there might be some slight differences
in the shape of the curve from one count to another due to statistical sampling.
Sizing of the WBC population is done simultaneously in an equal second matrix.
The highest “channel” represents a volume of ca. 400 fl. As with the RBC/PLT
sizing, the reproducibility of the curve is dependent upon the concentration of
(WBC) cells in the dilution.