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The red blood cell count on the routine CBC is the concentration of red cells, expressed in millions / µL of whole blood. While red cell counts can be performed by manual techniques, these are time-consuming and inaccurate. Automated counts are most commonly performed using "impedance counters" such as the Coulter Z2®, which we use for performing cell counts in body fluids. New methodology allows the counting of erythrocytes by flow cytometry. This is the technique used by our new hematology analyzer, the Advia. Impedance counters Flow cytometry counters
Last Updated: June 2000 |
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by drawing the cells through an aperture of the instrument. Each cell
causes a change in electrical resistance as it passes the aperture,
and this pulse is detected and amplified by the instrument. The sensitivity
can be adjusted so that platelets (smaller than red cells) are not counted;
WBC are counted as well as RBC, but white cell numbers (in thousands/µL)
are too low to cause significant error in the red cell count (in
millions/µL). The amplitude of the pulse is proportional to cell
size and, in some analyzers, such as the Heska bench top analyzer or
the Coulter S+IV, this is used for determining the MCV. The Coulter
Z2 (a bench-top impedance counter) is our back-up analyzer and only
performs cell counts (it does not provide an MCV). We use this cell
counter when our Advia is out of commission or inaccurate (in some dogs
with immune-mediated hemolytic anemia that have severe autoagglutination).
This is the standard instrument used for cell counts in body fluids,
other than blood, e.g. joint fluids, peritoneal fluids, because these
fluids cannot be analyzed through the Advia.
