procedures, test results may be misleading or even incorrect. It is important for the laboratory to provide appropriate and complete information to all clients in order to ensure quality patient care.
Safety
All fresh specimens should be handled carefully, since each specimen represents a potential source of infectious material. Safety precautions should include proper labeling of fixatives; specific areas designated for specimen handling (biological safety cabinets may be necessary under certain circumstances); proper containers for centrifugation; acceptable discard policies; appropriate policies for no eating, drinking, or smoking within the working areas; and, if applicable, correct techniques for organism culture and/or animal inoculation. In general, standard precautions as outlined by the Occupational Safety and Health Act must be followed when applicable, particularly when one is handling blood and other body fluids.
Collection of Fresh Stool Specimens
Stool specimens should always be collected before barium is used for radiological examination. Specimens containing barium are unacceptable for processing and examination, and intestinal protozoa may be undetectable for 5 to 10 days after barium is given to the patient. Certain substances and medications also interfere with the detection of intestinal protozoa; these include mineral oil, bismuth, antibiotics, antimalarial agents, and nonabsorbable antidiarrheal preparations. After administration of any of these compounds, parasites may not be recovered for one to several weeks. After the administration of barium or antibiotics, specimen collection should be delayed for 5 to 10 days or at least 2 weeks, respectively.
Collection Method
Fecal specimens should be collected in clean, wide-mouth containers; often a waxed cardboard or plastic container with a tight-fitting lid is selected for this purpose. The specimens should not be contaminated with water or urine because water may contain free-living organisms (including arthropod larvae and free-living nematodes) that can be mistaken for human parasites and urine may destroy motile organisms. Stool specimen containers should be placed in plastic bags for transport to the laboratory for testing. The specimens should be labeled with the following information: the patient’s name and identification number, the physician’s name, and the date and time the specimen was collected (if the laboratory is computerized, the date and time may reflect arrival in the laboratory, not the actual collection time). The specimen must also be accompanied by a request form indicating which laboratory procedures are to be performed; in some cases this information will be computerized and will be entered into the system on the nursing unit or in the clinic. Although it is helpful to have information concerning the presumptive diagnosis or relevant travel history, this information rarely accompanies the specimen. If such information is relevant and necessary to maximize diagnostic testing, the physician may have to be contacted for additional patient history.
Number of Specimens To Be Collected
Standard Approach
In the past, it has been recommended that a normal examination for stool parasites before therapy include three specimens, consisting of two specimens collected from normal movements and one collected after the use of a cathartic such as magnesium sulfate or Fleet’s Phospho-Soda. The purpose of the laxative is to stimulate some “flushing” action within the gastrointestinal tract. A cathartic with an oil base should not be used, and a stool softener (taken either orally or as a suppository) is usually inadequate for obtaining a purged specimen. The use of a laxative prior to collection of the third specimen is much less common than in years past. Also, if the patient already has diarrhea or dysentery, the use of any laxatives would be contraindicated.
When a patient is suspected of having intestinal amebiasis, collection of six specimens may be recommended. The examination of six specimens ensures detection of approximately 90% of amebic infections. However, considering cost containment measures, the examination of six specimens is rarely requested.
Different Approaches
During the past few years, recommendations regarding the collection, processing, and testing of stool specimens for diagnostic parasitology have been under review. New suggestions and options have arisen as a result of cost containment measures, limited reimbursement, and the elimination of mercury-based compounds for stool preservatives. The number of nonmercury preservative choices, collection systems, concentration devices, and immunoassays has increased dramatically.
It is important to realize that different laboratories will select different approaches. These differences should not be categorized as “right or wrong” or “acceptable or unacceptable”; they are merely different! To assume that there is only one correct approach for the examination of stool specimens is neither appropriate nor realistic. There are many factors to consider before selecting the approach for your own laboratory. In no particular order, some of the considerations include client base, physician ordering patterns, number of specimens received per month, cost, presence or absence of appropriate equipment, current and possible methodologies (including the new immunoassays such as enzyme immunoassay [EIA], fluorescent-antibody assay [FA], and rapid tests [membrane flow cartridge devices]), availability of expert microscopists, collection options, selection of preservativestain combinations, reimbursement issues, client education, area of the world where the laboratory is located, and emphasis on the most common infections (helminth or protozoa or both) seen in that geographic location.
When laboratory test menus are being developed, the pros and cons of the approaches selected need to be thoroughly understood, and diagnostic tests, potential results, and reporting formats should be carefully explained to all clients. As an example, if the results of a stool examination are based on a concentration sediment examination only, this information must be conveyed to the physician. Many of the intestinal protozoa are missed when this diagnostic test approach is used, and it is important for the physician to recognize the limitations of such testing. Most physicians receive very little, if any, exposure to medical parasitology in medical school, and many newer physicians trained as generalists or family practitioners also have limited parasitology training or experience (Table 3.1).
It is usually realistic to assume that patients are symptomatic if they are submitting stool specimens for diagnostic parasitology testing. In an excellent article by Hiatt et al., the premise tested was that a single stool specimen from a symptomatic patient would be sufficient to diagnose infections with intestinal protozoa. However, with additional stool examinations, the yield of intestinal protozoa from symptomatic patients increased dramatically (Entamoeba histolytica, 22.7% increase; Giardia lamblia, 11.3% increase; and Dientamoeba fragilis, 31.1% increase). This publication again demonstrates the problems associated with performing only a single stool examination (using the ova and parasite examination [O&P exam]). If the patient becomes asymptomatic after examination of the first stool specimen, it may be acceptable to discontinue the series of stool examinations (this should be a clinician decision).
Available options will be compared to the “gold standard,” which includes a series of three stool examinations (direct, concentrate, and permanent stained smear for a fresh specimen; concentrate and permanent stained smear for a preserved specimen). The single-specimen pros and cons are discussed in the previous paragraph (symptomatic versus asymptomatic patients). A suggestion has been made to pool three specimens and to perform a single concentration and a single permanent stained smear on the pooled specimen sample. Depending on the number of positives and negatives, this may be a viable
