[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

16
CHAPTER 2 Specimen Collection and Processing
In areas in which parasitic infections are not
considered a major cause of human disease, it
can be difficult for health care professionals to
recognize that these agents may be a cause of
the patient’s clinical condition. However, with
the increased number of populations at risk for
contracting parasitic infections, it is critical
for clinicians to obtain knowledge of the clinical
manifestations of parasitic diseases and
understand the appropriate laboratory test(s)
to order. Furthermore, laboratory technicians
must have an understanding of these diseases
to guide the physician in selecting the appropriate
tests. Because the diagnosis of these diseases
can be challenging and is not always straightforward,
it is imperative that strong communication
exist between the physician and clinical
laboratory.
This chapter is designed to introduce readers
to representative testing methods available for
the diagnosis of parasitic infections. Parasites
that may be determined using these testing
methods are identified. These lists are not
intended to be exhaustive in nature. By design,
appropriate testing methods are mentioned in
the specific parasite laboratory diagnosis sections,
which may or may not be noted in this
chapter.
Successful laboratory identification of parasites
requires the knowledge and practice of laboratory
testing in the preanalytic, analytic, and
postanalytic steps. For example, in the preanalytic
phase, a specimen received in the laboratory
that is compromised because of improper collection,
labeling, or transport should be rejected
and a new specimen requested. Similarly, laboratory
techniques performed in the analytic phase
of testing of these samples should be completed
with care to ensure that accurate results are
obtained. Interpretation and reporting of results
obtained, completed in the postanalytic phase of
testing, should be accurately reported in a timely
manner.
Specific topics addressed in this chapter
include the following: specimen collection and
handling guidelines for stool and intestinal specimens;
other specimen types, including tissue,
blood, and body fluids; immunologic testing;
future methods; and the reporting of results and
quality control associated with parasite studies.
A concise but comprehensive discussion of
each topic follows. This chapter contains
terminology that is detailed in other chapters
in this text. Reference to the appropriate
chapter is made where each appropriate term
first appears.
STOOL FOR OVA AND
PARASITE EXAMINATION
Without a doubt, the most common procedure
performed in the area of parasitology is the
examination of a stool specimen for ova and
parasites (abbreviated as O&P), where ova refers
to the egg stage of select parasites and parasites
encompasses the other morphologic forms that
may be present. There are two general components
associated with this routine parasitology
procedure macroscopic and microscopic examination.
The microscopic examination consists of
three possible components, each of which is
detailed in the sections that follow a discussion
of collection, transport, and fixatives for preservation.
As in all areas of laboratory testing, the
quality of the results is dependent on the appropriate
collection of the specimen.
Collection and Transport
Morphologic forms of protozoa and helminths
may be detected from a properly collected and
prepared stool specimen. When present, the protozoan
forms known as trophozoites and cysts
(discussed in more detail in Chapter 3) may be
recovered from these samples. Helminth stages,
such as eggs, larvae, proglottids, and adult
worms, may also be found. Definitions of these
helminth-related morphologic forms are detailed
in the corresponding parasite chapters of this
text (Chapters 8 to 11).
Because parasites are often shed (i.e.,
enter and subsequently passed in the stool)