DIAGNOSTIC INSIGHTS
Sponsored by an educational grant from IDEXX Laboratories
Choosing an in-house
hematology analyzer
Fred Metzger, DVM, DABVP
Metzger Animal Hospital
State College, Pa.
Impedance counters are based on the
beam, the pattern of light scattered by the
A complete blood count (CBC) is essential to
Coulter principle. The Coulter method of sizindividual cells records the cell size, nuclear
the assessment of the general health status
ing and counting particles is based on the
characteristics, and cytoplasmic contents,
of a patient and the evaluation of potential
change in resistance as the particles pass
providing a true optical 5-part leukocyte
underlying diseases. A CBC is an integral part
through
a
small
aperture
between
two
elecdifferential. Some analyzers provide an
of the diagnostic workup of every sick patient,
trodes. Because cells are classified on size
absolute reticulocyte count for the dog and
every preanesthetic examination, every senior
alone, not all WBCs can be differentiated
cat, which is the gold standard in classifying
or wellness profile, and every reevaluation of
from one another. Nucleated red blood
anemias. This technology may be slightly
patients with previous erythrocyte, leukocyte,
cells and clumped platelets are the same
more expensive than the other available
or platelet abnormalities.
relative size as leukocytes and may be mismethodologies and was previously limited
The advantage of getting immediate results
classified as WBCs and large platelets, or
only to reference laboratories.
and providing better patient care is motivatsmall clumps of platelets may be counted
The features of in-house hematology
ing more practices to invest in automated
as
erythrocytes.
analyzers
vary greatly. Practitioners should
hematology analyzers. Since the advent of the
Another significant issue with impedanceweigh the pros and cons of each instrument
Coulter counter 50 years ago, hematology
before deciding which one is most approprianalyzers have improved substantially, provid- based systems is that they require the use of
reagent fluids for normal instrument cycling
ate for the practice (Table 1). Regardless of
ing more accurate cell counts with automated
and involve a considerable amount of mainte- instrumentation, veterinarians should inter2-, 3-, or 5-part differential counts and requirnance and cleaning, which may increase the
ing considerably less technician time.
pret all analyzer results with a peripheral
price per test. Impedance analyzers are moder- blood film evaluation, which provides
In-house hematology analyzers can be
ately priced and provide fast results, but they
grouped according to technology into quantiinvaluable information about the cellular
cannot
provide
a
true
5-part
leukocyte
differtative buffy coat (QBC) analysis, impedance
morphologic changes that automated instruential or reticulocyte count.
counters, and laser flow cytometers. Because
ments cannot provide. Because hematologic
Laser flow cytometry is the most recent
hematology instrumentation can represent a
samples are particularly vulnerable to
and accurate automated cell analyzer technolsignificant investment for a veterinary pracchanges over time, in-house analyzers offer
ogy and the method used in most reference
tice, a strong knowledge of the underlying
the benefits of immediate and reliable inforlaboratories to determine the leukocyte differtechnology and capabilities of the various
mation for screening, diagnosing, and moniential count. As cells pass through a laser
analyzers is necessary to make the most
toring your patients’ health.
informed choice.
The QBC method classifies
Table 1: Comparing three types of in-house hematology analyzers
cells based on density and
staining of cellular compoLaser Flow Cytometer
Impedance or Focused-Flow Impedance
Quantitative Buffy Coat Profile
nents. Under high-speed cen5-part differential
3-part differential
WBC Differential
2-part differential
trifugation, blood separates
Neutrophils
Granulocytes
Lymphocytes/Monocytes (combined)
into plasma, the buffy coat
Lymphocytes
Lymphocytes
Granulocytes
Monocytes
Monocytes
(3-part differential for canine and bovine
(which contains white blood
Eosinophils
(Some systems estimate
samples with a significant number
cells [WBCs] and platelets),
Basophils
eosinophils and basophils.)
of eosinophils)
and the red blood cells. The
Yes
No
Absolute Reticulocyte Count
No, but reticulocyte % is reported.
QBC analyzers are easy-to-use
10 minutes
1 to 3 minutes
Sample Run Time
7 minutes
and very economical, require
little to no maintenance, and
are efficient at screening normal hematology samples. The
major disadvantages are the
inability to provide a full 5part differential because lymphocytes are grouped with
monocytes, and, in felines
and equines, the inability to
differentiate eosinophils,
which are reported in the
granulocyte count.
Nucleated RBC Interference
with WBC Count
No
Yes
No
Large Platelet Interference
with Cell Counts
No
Yes
No
Moderate
Minimal
Minimal
Run calibration rod daily.
Daily background counts
Weekly and/or monthly cleanings
(Some systems require 3-month, 6-month,
and yearly maintenance.)
Clean air filter weekly.
Yes (Review cell morphology, provide
5-part differential, validate data)
Yes (Review cell morphology, provide
5-part differential, validate data)
Yes (Review cell morphology,
validate data)
Technician Time for
System Run
Required Maintenance
Need for Peripheral Blood
Film Evaluation
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