[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 12 Artifacts and Confusers
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Size range: 12-20 m
FIGURE 12-3 Pollen grain.
FIGURE 12-1 Cluster of fat globule artifacts. (Courtesy
of Carolina Biological Supply Company.)
Average size: 15 m
FIGURE 12-2 White blood cell.
confusers are briefly discussed in the following
sections.
WHITE BLOOD CELLS
Polymorphonuclear white blood cells (WBCs),
which typically have an average size of 15 µm,
are often mistaken for amebic cysts, especially
those of Entamoeba histolytica, whose average
size range is 12 to 18 µm (Fig. 12-2).
WBCs are usually present in patients suffering
from ulcerative colitis, bacterial dysentery, or
intestinal amebiasis. Along with falling into the
amebic cyst size range, these WBCs have a twoto
four-lobed nucleus, similar in appearance to
the E. histolytica nucleus. Even though these
WBC lobes may appear as separate nuclei, they
are connected by thin chromatin bands. Protozoan
nuclear inclusions, such as karyosomes and
peripheral chromatin, are absent in WBCs.
Careful microscopic focusing is necessary because
these bands are often difficult to detect.
Mononuclear WBCs, also known as macrophages
or monocytes, may range in size from 28
to 62 µm (less on permanently stained preparations)
and closely resemble the E. histolytica
trophozoite, which measures 8 to 65 µm. Both
structures may ingest red blood cells (RBCs) and
debris, but only the macrophages ingest polymorphonuclear
WBCs. The macrophage has one
irregularly shaped nucleus that is often absent on
examination. Although the macrophage size
range overlaps that of E. histolytica, the macrophage
may be significantly smaller (5 to 10 µm).
Red-staining round bodies may be seen in the
macrophages.
POLLEN GRAINS
Thick-walled pollen grains resemble the eggs of
Taenia spp. but are smaller, measuring 12 to
20 µm (Fig. 12-3). Pollen grains may appear
round or symmetrically lobed. Unlike Taenia,
there are no notable interior structures.
Quick Quiz! 12-1
Which of the following findings can help differentiate
WBCs from amebic cysts? (Objective 11-1)
A. Size
B. Number of nuclei
C. Absence of protozoan nuclear inclusions
D. None of the above