Page 645 - Clinical Hematology_ Theory _ Procedures ( PDFDrive )

CHAPTER 30 ■ Instrumentation in Hematology 629
Classi cation of Anemias Based
TABLE 30.3 on Red Cell Distribution Width
and Mean Corpuscular Volume
MCV
RDW High Normal
High Macrocytic Normocytic
Normal Macrocytic Normocytic
,
RDW, red cell distribution width; MCV mean corpuscular volume.
Classi cation of Erythrocytes Based on MCV and
RDW
As long as the red cell volume distribution histogram is uni-
modal, erythrocyte size is described e ciently by the mean
(MCV) and coe cient o variation (RDW). An increased
RDW may occur with a low MCV even when the width o
the curve is normal.
Erythrocytes with a normal RDW are homogeneous in
character and exhibit very little anisocytosis on a periph-
eral blood smear. Erythrocytes with an increased RDW are
re erred to as heterogeneous and exhibit a high degree o
anisocytosis on a peripheral blood smear. A classi cation o
erythrocytes that includes the homogeneity or heterogeneity
o the erythrocytes in addition to the MCV and RDW values
has been proposed ( able 30.3).
The Leukocyte Histogram
Size-re erenced leukocyte histograms display the clas-
si ication o leukocytes according to size ollowing lysis.
It does not display the native cell size. he lytic reagent
causes a cytochemical reaction. As a result o the reaction,
the cytoplasm collapses around the nucleus, producing
di erential shrinkage. here ore, the histogram o leu-
kocyte subpopulations re lects the sorting o these cells
by their relative size, which is primarily related to their
nuclear size.
T e Coulter model system classi es approximately 20,000
particles when the leukocyte count is at the 10.0 × 10 cells/µL
level. As the leukocytes pass through the aperture in the
electrical impedance system, they displace their volume in
a conductive f uid, which causes a change in electrical resis-
tance as each cell passes through the aperture. T is change is
proportional to the cell volume. T e histogram generated by
the Coulter principle provides size in ormation.
Although the Coulter leukocyte histogram displays
all cells as small as 30 L, only those greater than 35 L are
counted as leukocytes. T e histogram di erentiates lym-
phocytes, mononuclear cells, and granulocytes (Fig. 30.11).
Mononuclear cells include blasts or other immature cells,
such as promyelocytes and myelocytes, as well as monocytes;
however, in a normal specimen, monocytes represent the
mononuclear cells.
s l
l e
c f o
. o
n
e
v i t
a
l
Re
Low
fL
Microcytic FIGURE 30.11 Electrical impedance leukocyte histogram. T ree
di erent cell types can be identi ed using the impedance prin-
Microcytic
ciple. Because the lytic agent acts on the cellular membrane and
cytoplasm and produces cellular shrinkage, these populations can
be distinguished rom one another. T e cellular population on
the extreme le represents lymphocytes, the middle population
represents mononuclear cells, and the population o cells on the
extreme right side represents granulocytes. (Adapted rom Pierre
R. Seminars and Case Studies: T e Automated Dif erential, Hialeah,
FL: Coulter Electronics, 1985:39, with permission.)
On the x-axis o the histogram, our regions are noted
at approximately 35, 90, 160, and 450 L. T ere are certain
expected characteristics o the curves at these locations. A
valley or depression should be seen between the lympho-
cytes and mononuclear cells and between the mononuclear
cells and granulocytes.
T e computer program uses these locations to determine
the three populations; however, each di erential analysis is
individualized to determine the position o the populations
in each specimen. Leukocytes normally occur at 35 L or
above; the region below 35 L should be clear. Particles such
as clumped or giant platelets, NRBCs, and nonlysed erythro-
cytes might produce inter erence at or below 35 L.
T e instrument detects abnormal patterns. T e types o
alert signals include the ollowing:
1. Cells below 35 L.
2. Cells between the lymphocyte and mononuclear cell
region. Lymphocytes that are larger than normal, such as
variant lymphocytes, certain blast orms, plasma cells, or,
in some cases, eosinophilia and basophilia, can trigger an
alert.
3. Cells between the mononuclear and granulocyte popula-
tions; an increase in IGs or other abnormal cell popula-
3
tions, such as certain types o blasts and eosinophils.
4. Cells to the ar right region o the curve, usually a high
absolute granulocyte count.
5. An abnormality detected at exactly the 35- L threshold.
6. A signi cant increase in the mononuclear population.
7. A multiple alert, when more than one o these regions is
a ected.
In AV di erential technology, there is a correlation o
signals to Di Plot populations (Figs. 30.12 and 30.13).
Lymphocytes are typically small with a regular shape. T ey
are smaller in volume and lower in absorbance than the other
cells and are positioned in the lower part o the Di Plot.
Neutrophils will absorb light depending on the presence o
cytoplasmic granules and segmented nuclei.