[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 2 Specimen Collection and Processing
Quick Quiz! 2-14
Which one of these parasites should be quantitated
in the parasitology report? (Objective 2-17)
A. Giardia intestinalis
B. Entamoeba coli
C. Trichomonas vaginalis
D. Blastocystis hominis
LOOKING BACK
Accurate detection of parasites requires appropriate
specimen collection and processing. This
preanalytic phase of the laboratory testing is
critical to a successful analysis. Because some
parasites will not survive outside the host, it
becomes necessary to collect certain specimens
into preservatives. The traditional test performed
on stool specimens is the O&P examination.
This consists of macroscopic and microscopic
examinations that include direct wet preparations,
concentration technique resulting in concentrated
wet preparations, and a permanent
stained smear. Stool screening methods are also
available for the detection of antigens of certain
protozoan parasites. There are situations when
other intestinal specimens (e.g., duodenal material,
sigmoidoscopy material, cellophane tape
preparation) are evaluated for the presence of
parasites. Many parasites do not reside in the
gastrointestinal tract but in other organs and
tissues. Specimens must be collected from the
appropriate sites and evaluated accordingly.
Finally, there are situations in which it is difficult
or impossible to demonstrate the parasite in the
laboratory, so immunologic assays are performed
to aid in the diagnosis.
The laboratory must complete the diagnostic
test by communicating the results effectively and
efficiently. This postanalytic process is just as
critical as the actual analysis. The physician must
understand the report to act appropriately for
the patient. All aspects of the parasitology laboratory
must follow the quality assurance guidelines
necessary for successful testing.
TEST YOUR KNOWLEDGE!
2-1. In the collection and transport of stool
specimens for parasites, which parasitic
stage is most affected by the length of time
from collection to examination? (Objective
2-2)
A. Cysts
B. Trophozoites
C. Oocysts
D. Helminth larvae
2-2. When using preservatives, what is the
appropriate ratio of fixative to stool?
(Objective 2-4)
A. One part fixative to one part stool
B. Two parts fixative to one part stool
C. Three parts fixative to one part stool
D. Four parts fixative to one part stool
2-3. One of the biggest disadvantages of formalin
as a fixative for O&P is that: (Objective
2-4)
A. It cannot be used for concentration
procedures.
B. It cannot be used for permanent stained
slides.
C. It cannot be used for direct microscopic
examinations.
D. It cannot be used for detecting protozoan
cysts.
2-4. Which of the preservatives contains mercuric
chloride? (Objective 2-4)
A. Formalin
B. SAF
C. PVA
D. Modified PVA
2-5. Trophozoites are found more often in
liquid stools rather than formed stools,
true or false. (Objective 2-5)
2-6. What is the purpose of using an ocular
micrometer? Explain why it must be calibrated.
(Objective 2-7)
2-7. A stool specimen is received in the laboratory
for an O&P examination in a twovial
system (formalin and PVA). The
laboratory technician on duty performs a
concentration procedure and prepares a
permanent stain slide but decides not to