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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4<br />
Blood Cell Identification<br />
Eosinophils exhibit the same nuclear characteristics <strong>and</strong><br />
the same stages <strong>of</strong> development as neutrophilic<br />
leukocytes. Immature eosinophils are rarely seen in the<br />
blood, but they are found in bone marrow smears. They<br />
may have fewer granules than more mature forms. The<br />
earliest recognizable eosinophilic form by light<br />
microscopy is the eosinophilic myelocyte. Eosinophilic<br />
myelocytes <strong>of</strong>ten contain a few dark purplish granules<br />
in addition to the orange-red secondary granules.<br />
Eosinophil, Any Stage With Atypical/<br />
Basophilic Granules<br />
Eosinophils with atypical/basophilic granules are<br />
typically the same size as their normal counterparts.<br />
Any stage <strong>of</strong> eosinophilic maturation may be affected<br />
<strong>and</strong> is more commonly seen in the promyelocyte <strong>and</strong><br />
myelocyte stage. The abnormal granules resemble<br />
basophilic granules <strong>and</strong> are purple-violet in color <strong>and</strong><br />
usually larger than normal eosinophilic granules at the<br />
immature stages. These atypical granules are usually<br />
admixed with normal eosinophilic granules in the<br />
cytoplasm. Although the atypical granules resemble<br />
basophilic granules they differ from normal basophilic<br />
granules by lacking myeloperoxidase <strong>and</strong> toluidine<br />
blue reactivity.<br />
Eosinophils with atypical/basophilic granules (also<br />
referred to as harlequin cells) are associated with<br />
clonal myeloid disorders <strong>and</strong> are most <strong>of</strong>ten seen in<br />
acute myeloid leukemia with the recurrent cytogenetic<br />
abnormality involving CBFB-MYH11, inv(16)(p13.1q22) or<br />
t(16;16)(q13.1;q22) <strong>and</strong> chronic myelogenous leukemia<br />
(CML).<br />
Mast Cell<br />
The mast cell is a large (15 to 30 μm) round or elliptical<br />
cell with a small, round nucleus <strong>and</strong> abundant<br />
cytoplasm packed with black, bluish black, or reddish<br />
purple metachromatic granules. Normal mast cells are<br />
differentiated from blood basophils by the fact that they<br />
are larger (<strong>of</strong>ten twice the size <strong>of</strong> blood basophils), have<br />
more abundant cytoplasm, <strong>and</strong> have round rather than<br />
segmented nuclei. The cytoplasmic granules are smaller,<br />
more numerous, more uniform in appearance, <strong>and</strong> less<br />
water-extractable than basophil cytoplasmic granules.<br />
Although both mast cells <strong>and</strong> basophils are primarily<br />
involved in allergic <strong>and</strong> anaphylactic reactions via<br />
release <strong>of</strong> bioactive substances through degranulation,<br />
the content <strong>of</strong> their granules is not identical. Both mast<br />
cell <strong>and</strong> basophil granules can be differentiated from<br />
neutrophilic granules by positive staining with toluidine<br />
blue in the former.<br />
Monocyte<br />
Monocytes are slightly larger than neutrophils, 12 to 20<br />
μm in diameter. The majority <strong>of</strong> monocytes are round<br />
with smooth edges, but some have pseudopod-like<br />
cytoplasmic extensions. The cytoplasm is abundant <strong>and</strong><br />
gray to gray-blue (ground-glass appearance) <strong>and</strong> may<br />
contain fine, evenly distributed, azurophilic granules<br />
or vacuoles. The nuclear-to-cytoplasmic ratio is 4:1 to<br />
2:1. The nucleus is usually indented, <strong>of</strong>ten resembling a<br />
three-pointed hat, but it can also be folded or<br />
b<strong>and</strong>-like. The chromatin is condensed, but less dense<br />
than that <strong>of</strong> a neutrophil or lymphocyte. Nucleoli are<br />
generally absent, but occasional monocytes may<br />
contain a small, inconspicuous nucleolus.<br />
Monocytes, Immature (Promonocyte,<br />
Monoblast)<br />
For purposes <strong>of</strong> pr<strong>of</strong>iciency testing, selection <strong>of</strong> the<br />
response “monocyte, immature (promonocyte,<br />
monoblast)” should be reserved for malignant cells in<br />
acute monocytic/monoblastic leukemia, acute<br />
myelomonocytic leukemia, chronic myelomonocytic<br />
leukemia, <strong>and</strong> myelodysplastic states. While normal<br />
immature monocytes may be identified in marrow<br />
aspirates, they are generally inconspicuous <strong>and</strong> don’t<br />
resemble the cells described in this section. The<br />
malignant monoblast is a large cell, 15 to 25 μm in<br />
diameter. It has relatively more cytoplasm than a<br />
myeloblast with the nuclear-to-cytoplasmic ratio<br />
ranging from 7:1 to 3:1. The monoblast nucleus is round<br />
or oval <strong>and</strong> has finely dispersed chromatin <strong>and</strong> distinct<br />
nucleoli. The cytoplasm is blue to gray-blue <strong>and</strong> may<br />
contain small, scattered azurophilic granules. Some<br />
monoblasts cannot be distinguished morphologically<br />
from other blast forms, hence the need for using other<br />
means (eg, cytochemistry <strong>and</strong> flow cytometry) before<br />
assigning a particular lineage to a blast cell.<br />
Promonocytes have nuclear <strong>and</strong> cytoplasmic<br />
characteristics that are between those <strong>of</strong> monoblasts<br />
<strong>and</strong> the mature monocyte discussed above. They are<br />
generally larger than mature monocytes, but they<br />
have similar-appearing gray-blue cytoplasm that <strong>of</strong>ten<br />
contains uniformly distributed, fine azurophilic granules.<br />
Cytoplasmic vacuolization is not a usual feature. The<br />
nuclei show varying degrees <strong>of</strong> lobulation, usually<br />
characterized by delicate folding or creasing <strong>of</strong> the<br />
nuclear membrane. Nucleoli are present but not as<br />
distinct as in monoblasts.<br />
Myeloblast, With Auer Rods<br />
Myeloblasts are the most immature cells in the myeloid<br />
series. They are normally confined to the bone marrow,<br />
where they constitute less than 3% <strong>of</strong> the nucleated<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>