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

Parabasal cells vary in size from 12 to 30 μm in diameter,
about a quarter to half the size of superficial squamous
cells. They tend to have a round to oval shape with
smooth borders and occasional small vacuoles in the
cytoplasm. They can appear in clusters and may be
angulated and have irregular polygonal shapes.
Their nuclei are round to oval and the nuclear- to-
cytoplasmic ratio is higher than seen in superficial
squamous cells.
Basal cells are rarely seen in vaginal smears unless a
pathologic process has damaged the squamous
epithelium. These cells are smaller than parabasal cells
and are round to oval in shape. They resemble very
small parabasal cells. They have scanty cytoplasm
and their nuclei are about the same size as those of
parabasal cells. However, due to their smaller size, basal
cells have a higher nuclear-to-cytoplasmic ratio than
parabasal cells.
Squamous Epithelial Cell
These large (30 to 50 μm) flat cells are derived from
the lining of the female vagina and cervix. In wet
preparation, squamous cells are about five to seven
times as large as a red cell and larger than parabasal
and basal cells. A single, small, condensed, round
or oval central nucleus about the size of a small
lymphocyte (10 to 12 μm) is seen in flat, round, or
rectangular cells. There may be fine cytoplasmic
granulation. The edges of the cell may be curled. The
cell membrane is usually well-defined in brightfield and
phase microscopy. Degenerating squamous cells show
granular swollen cytoplasm and eventual fraying; the
nucleus becomes pyknotic and then lyses, and the cell
may eventually resemble an amorphous disintegrating
mass.
Spermatozoa
In wet preparations, the sperm head is about 4 to 6 μm
long, usually tapering anteriorly. It is smaller and
narrower than red cells. Slender tails are about 40 to
60 μm long. The head may be separated from the tail,
making identification more difficult.
Fern Test
Evaluation of an air-dried slide prepared from the
vaginal pool is one of the most widely used tests to
detect rupture of the amniotic membranes and the
early onset of labor. When properly performed and,
particularly if used in conjunction with another widely
used test such as the nitrazine test, this is highly sensitive
and specific for the detection of ruptured membranes.
Clinical Microscopy Miscellaneous Cell
The “fern test” was initially described in 1955 and its ease
of use and clinical utility has been confirmed by multiple
published studies.
A sample of fluid is collected from the vaginal pool and
allowed to air dry on a microscope slide for five to seven
minutes. This is then examined under the microscope
at low power. A positive test, indicating the presence
of amniotic fluid, consists of an elaborate arborized
crystallization pattern (ferning) best visualized when
the substage condensor is lowered to accentuate the
diffraction pattern. The test may be positive as early as
12 weeks of gestation. Common contaminants such as
blood, urine, meconium (by itself indicative of ruptured
membranes), semen, or alkaline antiseptic solutions
that may be present in the vagina do not usually cause
a falsely negative result unless present in very high
concentrations. Inadvertent contamination of the
specimen by cervical mucus may cause a falsely
positive result but the arborization pattern is less
elaborate and normally will not form after the first
trimester of pregnancy due to high levels of
progesterone present.
Organisms
Trichomonas
Trichomonas vaginalis primarily causes vaginal infection,
but also is capable of infecting the urethra, periurethral
glands, bladder, and prostate. The normal habitat of
T. vaginalis is the vagina in women and the prostate
in men. In women, the organism feeds on the
mucosal surface of the vagina, ingesting bacteria and
leukocytes.
T. vaginalis is a protozoan flagellate with only a
trophozoite stage. It is pyriform or pear-shaped with
a length of 7 to 23 μm. There is a single nucleus and a
stout central axostyle protruding from the posterior end
of the body. Additional morphologic features include
four anterior flagella and an undulating membrane in
the anterior half from which projects a single posterior
flagellum. In wet mounts, it demonstrates a jerky,
rotating, nondirectional leaf-like motion. Rippling of the
undulating membrane can be seen for several hours
after cessation of organism motility.
Yeast/Fungi
Candida albicans is a colorless, ovoid, 5 to 7 μm,
thick-walled cell. A cell with a single bud is
characteristic. The cells stain poorly with aqueous stains
in wet preparations, but are strongly positive with Gram
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