Vaginal secretions or exudates may be directly examined for the
presence of yeast, Trichomonas vaginalis, or clue cells by using saline
wet mounts (Stamm, 1988). KOH mounts are used to dissolve surrounding mucus
or tissue for easier examination of specimens for yeast or fungal elements.
In addition, a characteristic amine odor may be observed in patients with bacterial
vaginosis and T. vaginalis when vaginal secretions are combined with
10% KOH. Vaginal pH greater than 4.5 also indicates presence of bacterial vaginosis
or trichomoniasis.
Specimen Collection
Vaginal secretions and other appropriate specimens should be
collected on a swab, which may be used for immediate examination. If the swab
is placed in approximately 1 mL of sterile saline in a small test tube, this
saline solution may be used for the wet prep and KOH prep. For determination
of vaginal pH, touch pH paper to vaginal wall or to discharge in speculum.
Avoid contact with cervical mucus because it has a high pH. Match pH paper
to color scale to determine the pH value.
Procedure
Emulsify the specimen by immersing the end of the swab
into the tube containing saline to make a heavy suspension.
Place specimen on a slide and cover with a coverslip carefully
to avoid trapping air bubbles under the coverslip.
Examine the slide immediately for the presence of yeast, trichomonads,
or clue cells. Scan first on low power with reduced light; Trichomonads can
often be identified on low power. Switch to high power to check for the presence
of yeast cells, pseudo hyphae, clue cells, or less vigorously motile trichomonads.
A KOH prep may be needed to better examine for yeast in purulent specimens.
The KOH prep is made by placing the specimen on a slide, adding
10% KOH, and mixing with a wooden applicator or swab. Cover with a coverslip
and avoid trapping air bubbles. Sniff for a "fishy" odor.
Use low power to scan for yeast and confirm on high power.
Examination of Slide and Interpretation of Results
Trichomonads are only seen in the saline prep; they are lysed
(broken down) by KOH. They have ameboid properties, are generally ovoid, slightly
larger than polymorphous nuclear leukocytes (PMNs), and in fresh preparations
are recognized by their jerky, swaying movement. The presence of even one organism
is diagnostic. Actively motile trichomonads are easily seen on low power. High
power is necessary to detect less vigorously moving organisms when only the
flagella or undulating membrane may be in motion. Numerous PMNs are often present.
Numerous "clue" cells and few or no PMNs are indicative
of bacterial vaginosis. "Clue cells" are irregularly bordered squamous
epithelial cells whose cell outlines are obliterated by sheets of small bacteria. "Clue" cells
are seen in saline, not KOH preps.
Yeast may be obscured by epithelial cells in the saline wet
mount, but pseudo hyphae and budding yeast cells are sometimes visible. PMNs
may or may not be visible. In the KOH preparation, budding yeasts and pseudo
hyphae are more easily seen because epithelial cells and PMNs have been lysed.
Use low power to scan for yeasts and confirm on high power. Care should be
taken in interpreting apparent results; artifacts are common in KOH preps as
a result of cell degeneration, air bubbles, crystallization, and glycerol.
Sources of Error
The following errors in technique will decrease the sensitivity
of the wet mount for detection of T. vaginalis:
Collection of the specimen from the endocervix
The use of cool saline (saline should be at room temperature).
Delay in reading the smear
Contamination of the saline prep with KOH
Too much saline on the slide, causing the material to move
rapidly across the field
Making a preparation too thick
Failure to read the slide with condenser lowered (too much
light)
Centers for Disease Control and Prevention
1600 Clifton Rd, Atlanta, GA
30333, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348, 24 Hours/Every Day cdcinfo@cdc.gov
Program Operations Guidelines for STD Prevention
