Page 279 - parasitology for medical and clinical laboratoryprofessionals

Laboratory Procedures for Identifying Parasitic Organisms and Their Ova 259

PROCEDURE 12-1

INITIAL WET MOUNT
Clinical Rationale

There are three specific steps in performing the fecal samples for routine micro-
scopic evaluation. The wet mount is a preliminary and direct procedure that will not

only sometimes yield identification of certain parasites, but will enable visualization
of WBCs or RBCs. The direct wet mount is the initial and perhaps the most important
step and is used as a screening test in which trophozoite motility can be observed.
The wet mount is followed by the second step, that of a concentration method pro-
cedure which affords the greatest opportunity for recovering parasite eggs or organ-
isms. The third step involves preparation of and staining of permanent stains that
are prepared from concentration methods. The process of staining shows important

identification features such as intracellular components that include nuclei, organ-
elles, and ingested materials, and a variety of stains are available for staining various
features characteristic of the various organisms.
In diarrheal stools, trophozoites may be active and easily viewed with details that
will provide an early diagnosis and therefore quicker treatment for the patient.
Negative wet mounts should be followed by concentration procedures and the making
of permanent stains of the feces for microscopic examination. Only fresh stools are used
for the direct wet mount, while motile trophozoites will still be able to be viewed by the
laboratory professional. The smear should be thin enough that a printed page such as a
newspaper can be read through the mixture. Air bubbles should be avoided and the slide
should be viewed systematically in order to cover the entire slide. The light source should
be carefully adjusted, as some protozoa are colorless, by using the condenser and the iris
diaphragm of the microscope to ensure that all details of the slide such as WBCs, RBCs,
yeast, and the organisms are able to be seen. A systematic manner of viewing the slide
should be employed to insure complete coverage of each slide (Figure 12-5).

Delmar/Cengage Learning

FIGURE 12-5 Systematic pattern for examining
direct wet mount

Equipment and Supplies
1. Protective gloves and disposable gown
2. Standard microscope slides
3. Applicator sticks for obtaining and mixing saline and fecal material
(continues)