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Laboratory Procedures for Identifying Parasitic Organisms and Their Ova 263

Concentration methods are necessary in most examinations as the numbers of
organisms present may be few. Several prepackaged kits are available for preparing
the stool sample in the second process of a complete examination of a fecal speci-
men. However, these commercially prepared kits are more expensive than using
bulk reagents and supplies. These kits are used most often for convenience, ease of
cleaning of the environmental surfaces, and the substitution for some of the volatile
formalin-ether mixture. It is possible to use both fresh and preserved stool specimens
when performing a concentration procedure.
Because concentration processes enhance the chances of finding parasites, this is

the second step following the initial wet mount to be performed in a complete analysis of
a stool sample, and is preparatory to performing a sedimentation or fl otation technique.
Concentration procedures serve to increase the density of the parasites from a speci-
men into a small amount of liquid from which much of the fecal debris is also removed,
leaving a clear view of the contents of the concentrating tube. It should be noted that
trophozoites of protozoans are destroyed during this process, but cysts of protozoa and
the larvae and eggs of helminthes are frequently found when using this technique.

It is often necessary to use both the sedimentation and flotation procedures for
performing concentration techniques designed to increase the numbers of organ-
isms or ova that may be present. The two methods accomplish basically the same
goal but one may be more useful than the other depending upon the species of para-
site or parasites present. Both of these methods are based on differences between

the specific gravity, which is best described as the density of a solution based on
dissolved materials, to consolidate the organisms or ova into a smaller area. In the
sedimentation procedure, organisms and ova are compacted into the bottom of a
conical-shaped centrifuge tube. Flotation methods serve to suspend the organisms
and ova at the top of a solution of great density. The sedimentation method tends to
give a greater diversity of organisms and their various stages as well as eggs and
concentrates a large amount of feces into approximately 2 grams of sediment. The

flotation method is primarily advantageous for concentrating the ova, but other stages
and forms may also be found with this method.
Equipment and Supplies
1. Protective gloves and disposable gown
2. 15 mL conically shaped glass centrifuge tubes
3. Applicator sticks for obtaining and mixing saline and fecal material
4. 10% formalin
5. Saline for washing samples
6. Method for straining feces such as dampened surgical gauze that will allow ova
and parasites to pass through but will retain large fecal debris (care should be
exercised in mucoid sample, where oocysts and microsporidia may be trapped
in the mucus).
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