[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 2 Specimen Collection and Processing
request these tests. For example, in a patient with
diarrhea who has returned from a camping trip,
tests for Giardia and Cryptosporidium are indicated.
If other parasites are potentially causing
the patient’s symptoms, a complete O&P examination
must be performed. It is recommended
that O&P examinations and fecal immunoassays
be available in the laboratory test options. Some
of the kits require fresh or frozen stool and
cannot be done on preserved specimens. This is
difficult for many laboratories because they
receive their stool specimens in preservative vials.
The procedure of the specific kit must be followed
carefully for accurate results.
Quick Quiz! 2-8
What is one advantage of the stool screening method?
(Objective 2-11)
A. It is highly sensitive and specific.
B. It can detect all parasites.
C. It can be performed on fresh or preserved
specimens.
D. It is labor-intensive.
OTHER INTESTINAL SPECIMENS
In certain intestinal parasitic infections, examination
of stool specimens may not detect the infectious
agent. There are additional procedures that
can be performed to reveal the presence of specific
parasites. These are often used when the
physician suspects a particular parasite and the
traditional O&P examination is negative. These
procedures include examination of duodenal
material, examination of sigmoidoscopy material,
and using cellophane tape to detect pinworms
(Chapter 8).
Duodenal Material
Parasites that reside in the small intestine may be
more difficult to recover in a stool specimen. In
these situations, examining material from the
duodenal area may yield success. The specimen
may be collected by nasogastric intubation or by
the enteric capsule test (Enterotest). Parasites
that may be observed in this type of specimen
include Giardia intestinalis trophozoites, Cryptosporidium
spp., Isospora belli, Strongyloides
stercoralis (Chapter 8), and eggs of Fasciola
hepatica or Clonorchis sinensis (Chapter 11).
Duodenal fluid must be examined promptly
because if there are trophozoites present, they will
deteriorate rapidly. The material can be examined
microscopically as a wet preparation. If the
volume of fluid is sufficient (>2 mL), it should
be centrifuged and the sediment examined. The
material can be mixed with PVA fixative; stained
slides can be prepared using trichrome, iron
hematoxylin, and/or modified acid-fast stain. The
material can also be used to perform antigen tests
for Cryptosporidium and/or Giardia.
The Enterotest is a simpler method for collecting
duodenal material without requiring intubation.
The patient swallows a gelatin capsule that
contains a coiled length of yarn. The capsule dissolves
in the stomach and the weighted string is
carried to the duodenum. The free end of the
string is attached to the patient’s neck or cheek
with tape. After a 4-hour incubation period, the
yarn is pulled back out of the patient. The bilestained
mucous material brought up on the string
is then examined microscopically via wet preps
and, if necessary, permanent stains.
Sigmoidoscopy Material
Examination of sigmoidoscopy (colon) material
is often helpful for detecting E. histolytica. Material
from ulcers obtained by aspiration or scraping
should be examined by direct wet preparations
and permanent stains. It is important to realize
that if E. histolytica is present, the trophozoite
stage will often be present and timing is critical
because of the fragility of this organism. Coccidian
parasites and microsporidia (Chapter 7) may
also be recovered from examining material from
the sigmoid colon.
Colon biopsy material may also be collected
for examination. The specific methods necessary
to perform on this biopsy material vary by
the organism suspected. For example, samples