Hematology and Clinical Microscopy Glossary - College of American ...

Artifacts
A variety of artifacts can be identified in a bone marrow
aspirate. They may be due to fixation, biopsy technique
or due to specimen processing.
EDTA: If a specimen is anticoagulated with EDTA
and there is a delay in the preparation of smears,
artifacts can appear in the cells. These can include the
appearance of dyserythropoiesis with nuclear lobulation
and fragmentation as well as cytoplasmic vacuoles.
Neutrophils Necrobiosis (Degenerated Neutrophils):
Neutrophil necrobiosis is a common phenomenon that
can be seen both in normal individuals and in patients
with a variety of medical conditions, including
infections, inflammatory disorders, and malignancies.
It is nondiagnostic and nonspecific. Degenerated
neutrophils are generally easily identified because they
resemble normal segmented neutrophils. They are round
to oval cells ranging from 10 to 15 μm and their N:C
ratio is 1:3 or less. The major distinguishing feature is that
the nucleus shows karyorrhexis and/or pyknosis. These
changes are appreciated when a cell with neutrophilic
granules (pale pink cytoplasm with fine lilac granules)
contains multiple, unconnected nuclear lobes
(karyorrhexis) or a single, dark, round to oval nucleus
(pyknosis). The chromatin is dense and homogeneous
without visible parachromatin or nucleoli. The nuclear
lobes may fragment into numerous small particles of
varying size that can resemble microorganisms such
as bacteria or fungi. Also, the nuclear outlines may
become indistinct and blurred. As the cellular
degeneration continues, the cytoplasm will become
hypogranulated, then agranular, and the cytoplasmic
borders may become frayed and indistinct. Sometimes,
the cells will contain scattered larger azurophilic or
dark blue granules (toxic granulation). Vacuolation is
frequent. If a cell is too degenerated to be recognized
as a neutrophil and lacks recognizable cytoplasm, one
should identify it as a basket/smudge cell. On occasion,
necrobiotic neutrophils can contain ingested bacteria
or fungi. However, the microscopist must be very careful
when making this identification since nuclear fragments
may appear similar and deceive the observer.
Other cells that may resemble degenerated neutrophils
are nucleated red cells in the blood and orthochromic
normoblasts in the bone marrow. These cell types have
pinkish orange, agranular cytoplasm and a single, often
eccentric nucleus with dense chromatin and very little
to no parachromatin.
Specimen processing/suboptimal staining: If the slides
are fixed before adequately drying, cellular outlines can
Bone Marrow Cell Identification
appear indistinct and the nucleus can appear to be
leaking into the cytoplasm. Uptake of water in methanol
when used in fixation can cause red blood cells to
appear refractile with sharp round inclusions.
Overstaining or understaining of aspirate smears can
result in erroneous cell identification. Stain precipitate on
the slides may be due to unclean slides or improper
drying of the stained smears. Contaminated stain
components may result in the presence of bacterial
or fungal organisms in the smear but are typically
extra cellular.
Technique: If the aspirate specimen is partially clotted
before smears are made, small clots can be mistaken
for spicules and may lead to inaccurate assessment
of cellularity or erroneous determination of absent iron
stores with iron stains. Extensive platelet clumping can
also mimic spicules and hinder cell distribution and
staining. Thick smears may result in poor staining of
cells and poor cytologic detail.
Miscellaneous
Blast Cell
Squamous epithelial cells and endothelial cells are A
blast is a large, round to oval cell, 10 to 20 μm in diameter.
The nuclear-to-cytoplasmic ratio is high, approximately
7:1 to 5:1. The blast often has a round to oval
nucleus, but sometimes is indented or folded, and has
fine, lacy, reticular chromatin. One or more prominent
nucleoli may be seen. The cytoplasm is basophilic and
agranular.
The morphologic features of a blast cell do not permit
determination of the cell lineage. The one exception
is the presence of Auer rods, which are diagnostic
of myeloid lineage (i.e., myeloblast, see the entry for
“Myeloblast with Auer rod”). Other cells that may have
the appearance of a blast include lymphoblasts and
some lymphoma cells. In the absence of Auer rods,
immunophenotyping by flow cytometry (or immunohistochemistry
on tissue sections) or cytochemical staining
(eg, peroxidase or Sudan black B reactivity) is required
to determine the lineage of a given blast cell.
Lymphoblasts are the most immature cells of the lymphoid
series. They are most commonly seen in acute
lymphoblastic leukemia (ALL) and lymphoid blast crisis
of chronic myelogenous leukemia (CML). Lymphoblasts
are widely variable in appearance, even at times within
a single case, ranging from 10 to 20 μm in diameter with
an N:C ratio ranging from 7:1 to 4:1. The broad
morphologic spectrum of lymphoblasts permits their
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