Hematology and Clinical Microscopy Glossary - College of American ...
Hematology and Clinical Microscopy Glossary - College of American ...
Hematology and Clinical Microscopy Glossary - College of American ...
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12<br />
Blood Cell Identification<br />
more frequently seen in elderly women. Red cell<br />
agglutinates can also be found in cases <strong>of</strong> paroxysmal<br />
cold hemoglobinuria that exhibit a similar clinical<br />
pattern <strong>and</strong> can occur after viral infections. This disorder<br />
is caused by an IgG antibody that binds to the red cells<br />
at low temperature <strong>and</strong> then causes hemolysis when<br />
the blood is warmed to 37° C.<br />
Rouleaux<br />
Rouleaux formation is a common artifact that can be<br />
observed in the thick area <strong>of</strong> virtually any blood film. This<br />
term describes the appearance <strong>of</strong> four or more<br />
red blood cells organized in a linear arrangement<br />
that simulates a stack <strong>of</strong> coins. The length <strong>of</strong> this<br />
arrangement (18 μm or more) will exceed its width<br />
(7 to 8 μm), which is the diameter <strong>of</strong> a single red cell.<br />
The central pallor <strong>of</strong> the red cells is generally apparent,<br />
but it may be obscured due to overlapping <strong>of</strong> the cells’<br />
cytoplasm. When noted in only the thick area <strong>of</strong> a<br />
blood film, rouleaux formation is a normal finding<br />
<strong>and</strong> not associated with any disease process. True<br />
rouleaux formation is present when this artifact is seen<br />
in the thin area <strong>of</strong> a blood film. It is <strong>of</strong>ten associated<br />
with a proteinaceous, blue-staining background. True<br />
rouleaux formation is due to increased amounts <strong>of</strong><br />
plasma proteins, primarily fibrinogen, <strong>and</strong> globulins.<br />
It is seen in a variety <strong>of</strong> infectious <strong>and</strong> inflammatory<br />
disorders associated with polyclonal increases in<br />
globulins <strong>and</strong>/or increased levels <strong>of</strong> fibrinogen.<br />
Rouleaux formation associated with monoclonal<br />
gammopathies can be seen in multiple myeloma<br />
<strong>and</strong> in malignant lymphomas such as Waldenstrom’s<br />
macroglobulinemia.<br />
Lymphocytic <strong>and</strong><br />
Plasmacytic Cells<br />
Lymphoblast<br />
Lymphoblasts are the most immature cells <strong>of</strong> the<br />
lymphoid series. They are most commonly seen in acute<br />
lymphoblastic leukemia (ALL) <strong>and</strong> lymphoid blast crisis<br />
<strong>of</strong> chronic myelogenous leukemia (CML). These round<br />
to oval cells range in size from 10 to 20 μm. The N:C ratio<br />
varies from 7:1 to 4:1. Morphologically, lymphoblasts are<br />
variable in appearance, even at times within a single<br />
case. On one end <strong>of</strong> the spectrum, L-1 lymphoblasts<br />
are small cells with dense but not clumped chromatin,<br />
inconspicuous or absent nucleoli, <strong>and</strong> extremely<br />
scanty cytoplasm. On the other end are L-2<br />
lymphoblasts that are large cells with finely dispersed<br />
chromatin, variable numbers <strong>of</strong> distinct basophilic<br />
nucleoli, <strong>and</strong> moderate amounts <strong>of</strong> cytoplasm, closely<br />
resembling myeloblasts. The nuclear contours <strong>of</strong><br />
lymphoblasts range from round to convoluted. The<br />
cytoplasm is typically slightly to moderately basophilic,<br />
<strong>and</strong> is usually agranular. Auer rods are absent. Because<br />
lymphoblasts are quite variable in appearance, it is<br />
<strong>of</strong>ten impossible to correctly classify an individual cell<br />
based on the morphology alone. Lymphoblasts can<br />
be indistinguishable from other types <strong>of</strong> blasts <strong>and</strong><br />
lymphoma cells. For purposes <strong>of</strong> pr<strong>of</strong>iciency testing,<br />
one should identify individual cells exhibiting this<br />
immature type <strong>of</strong> morphology as blast cells.<br />
Lymphocyte, Normal<br />
While most lymphocytes are fairly homogeneous, they<br />
do exhibit a range <strong>of</strong> normal morphology. Lymphocytes<br />
are small, round to ovoid cells ranging in size from 7 to 15<br />
μm with an N:C ratio ranging from 5:1 to 2:1. Most lymphocytes<br />
have round to oval nuclei that may be slightly<br />
indented or notched. The chromatin is diffusely dense or<br />
coarse <strong>and</strong> clumped. Nucleoli are not<br />
visible, although some cells may exhibit a small, pale<br />
chromocenter that may be mistaken for a nucleolus.<br />
Most lymphocytes have a scant amount <strong>of</strong> pale blue<br />
to moderately basophilic, agranular cytoplasm.<br />
Occasionally, the edges may be slightly frayed or<br />
pointed due to artifacts induced during smear<br />
preparation. Occasional lymphocytes will have a small<br />
clear zone, or h<strong>of</strong>, adjacent to one side <strong>of</strong> the nucleus.<br />
Lymphocyte, Large Granular<br />
Large granular lymphocytes are medium to large cells<br />
with round nuclei, dense chromatin, <strong>and</strong> no visible<br />
nucleoli. The cytoplasm is moderate to abundant, clear<br />
or lightly basophilic, <strong>and</strong> contains several coarse,<br />
unevenly distributed, small azurophilic granules. These<br />
cells are found in small numbers in blood smears from<br />
normal individuals, but may be increased in association<br />
with reactive lymphocytes. Cell surface marker studies<br />
show that these cells are either natural killer cells or<br />
suppressor/cytotoxic T lymphocytes.<br />
Lymphocyte, Reactive (Includes<br />
Plasmacytoid <strong>and</strong> Immunoblastic Forms)<br />
The key distinguishing feature <strong>of</strong> reactive<br />
lymphocytes is their wide range <strong>of</strong> cellular sizes <strong>and</strong><br />
shapes, as well as nuclear sizes, shapes, <strong>and</strong> chromatin<br />
patterns. These cells are reacting to an immune stimulus<br />
<strong>and</strong> are frequently increased in viral illnesses. The<br />
classic example is infectious mononucleosis (acute<br />
Epstein-Barr virus infection). Reactive or atypical<br />
lymphocytes can also be found in a variety <strong>of</strong> other viral<br />
<strong>College</strong> <strong>of</strong> <strong>American</strong> Pathologists 2012 <strong>Hematology</strong>, <strong>Clinical</strong> <strong>Microscopy</strong>, <strong>and</strong> Body Fluids <strong>Glossary</strong>