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Clinical Pathology Laboratory - Available
Test
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Advia 2120 Hematology Analyzer
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| The Advia 2120 is the new hematology analyzer in Clinical Pathology
(in operation as of April 2008). It is based solely on flow cytometric
principles. With the Advia, blood is
passed through a laser, which counts cells and determines their size
by the angle of scattered light. |
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Platelet Counts |
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With the Advia, platelets are distinguished from red cells by their
small size and light scatter properties. The Advia provides very accurate
platelet counts in most species. In addition, it can detect platelet
clumps and flags their presence when they are over a certain number.
We incorporate this flag with the results to indicate that the provided
platelet count is actually the minimum number (because clumps lower
the count). Platelet counts are always lower than they really are
(in vivo) in samples with clumping, regardless of the method (manual
or automated) used to obtain the count. In some instances, there are
so many platelet clumps that the count is totally inaccurate from
the Advia. In these cases, counts are not provided but an estimate
of platelet numbers from the smear is still provided (for those tests
that include a blood smear examination). Cats are notorious for platelet
clumping (their platelets are activated at the slightest provocation)
and it is difficult to obtain accurate counts in this species.
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| Platelet clumping is usually due to a sample collection
problem and can be minimized by collecting blood from a large peripheral
vein (cephalic or jugular), such that blood flows smoothly into the
vacutainer or syringe, and using a 22 or 23 g needle (in a dog or
cat). The blood should be mixed with the anticoagulant as soon as
possible after collection, by gentle rotation or inversion. Platelet
clumping increases with time, so platelet counts should be done as
soon as possible after collection to maintain accuracy. In rare instances,
clumping can be due to an EDTA-dependent antibody in the patient's
blood. In these cases, accurate counts can only be obtained with samples
collected into citrate (heparin causes clumping of platelets from
animals). |
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Reticulocyte counts |
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| The Advia can measure reticulocytes by flow cytometry.
Reticulocyte counts are quite accurate in the dog and all reticulocyte
counts (whenever possible) are done with the Advia in this species.
Reticulocyte counts in cats are still performed manually by counting
the number of reticulocytes in new methylene blue-stained smears. |
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Differential cell counts |
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| The Advia also provides a differential cell count in
certain species (dogs, cats, horses, cattle, sheep, pigs, monkeys,
rats, mice, goats). This is accomplished by staining the white cells
with peroxidase and separating them on the basis of the amount of
peroxidase staining and cell size. The leukocytes are separated into
different cell clusters, corresponding to neutrophils, eosinophils,
lymphocytes, monocytes, and large unstained cells (LUCs). Large unstained
cells are usually large (or reactive) lymphocytes or monocytes, however
blasts (in leukemic patients) are also LUCs. Basophils are counted
separately in a different (basophil) channel as they will not stain
with peroxidase. For more information on differential cell counts
from the Advia, refer to the automated CBC. |
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Correlations |
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| Correlations have been done in our laboratory in both
sick and healthy animals between our old S+IV hematology analyzer
and the Advia. The methods correlate quite well, although some differences
are apparent (and to be expected) between the Advia and S+IV results.
The most notable differences are higher HCTs, RBC counts and MPVs
and lower MCVs (especially equine and ruminant species) with the Advia
compared to the S+IV. |
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