SPECIMEN COLLECTION AND HANDLING The usual diagnostic stages of intestinal parasites are helminth eggs and larvae and protozoan trophozoites and cysts. Specimens obtained for diagnosis should be collected and handled so that these stages, when present, will be identifiable when the specimens reach the laboratory. In fact, reliable diagnoses of parasitic diseases begin with satisfactory materials, and the importance of properly collected specimens cannot be overemphasized. Inadequate samples and old or poorly preserved materials are usually of little or no value in establishing a diagnosis and may lead to erroneous conclusions. The most common type of body material submitted for parasitologic examination is feces, but other materials such as sputum, urine, aspirates, tissue scrapings, and specimens obtained by biopsy may be submitted in certain cases. FECAL SPECIMENS •COLLECTION NORMALLY PASSED SPECIMENS To obtain satisfactory material for examination, adequate instructions and proper containers for collecting fecal specimens must be provided. Persons who have little or no knowledge of the proper procedures for submitting samples to the laboratory often make the collections; therefore, complete and explicit directions should be given to the person responsible for obtaining the specimen. Printed instructions with line drawings to illustrate certain steps are often included in the collection kits the laboratory supplies. In hospitals or clinics, brief but specific directions should be supplied to ward or nursing stations. Specimens for diagnosis may be divided into three categories: 1) those received directly from hospitalized patients; 2) those submitted by outpatients; and 3) those shipped or mailed to the laboratory. In hospital or clinic laboratories, most patient specimens fall into the first two categories, although proficiency testing specimens may be received by mail. Public health and reference laboratories most often receive shipped specimens. The criteria for satisfactory material are essentially the same for all three categories, but the method of submission, described in the section on Transportation and Preservation, will vary. In collecting fecal specimens, several factors should be considered: type of container, size and age of the specimen, and substances that might interfere with examinations. The container should be clean, dry and sufficiently large to accommodate a sample of adequate size. It should also be leakproof, with a tight-fitting lid to prevent spills. A half-pint waxed cardboard carton with an operlapping lid is recommended for routine collection (fig. 1). This type of carton can be defecated into directly, does not leak, and permits labeling directly on the box. Plastic cups of similar size with snap-in lids are also satisfactory. Larger sizes of both types of containers are available. Feces should be passed directly into the container or on clean paper and transferred to the container for transporting to the laboratory. In hospitals, specimens may also be collected in bedpans if the feces are not contaminated with urine. Information identifying the patient and the date and hour of passage should be recorded on the carton or should accompany the specimen. The time of passage is especially important, since trophozoites soon die outside the body and other stages may undergo changes that would hamper identification. Ideally, unpreserved specimens should arrive in the laboratory within 1 to 2 hours after passage. Older specimens, especially if they contain trophozoites, may be erroneously reported as negative. A suggested identification label for specimen containers is as follows: To permit adequate macroscopic and microscopic examination, the entire fecal passage should be submitted to the laboratory. This not only provides sufficient material for several techniques, but allows the technologist to select a particular portion of the stool for examining. For example, soft or mucoid material is preferred for preparing smears for staining and more formed portions are used for concentration. Since organisms inhabiting the lower colon may often be present in the outer layer of the fecal bolus, having the entire stool will allow the technologist to scrape material from the surface for examining. Surface material is often useful in diagnosing Schistosoma mansoni and Entamoeba histolytica infections. If the entire fecal specimen cannot be submitted, a quantity of about 20 to 30 grams (the size of a medium-size walnut, if formed, or 2 to 3 tablespoonsful, if loose or watery) should be provided to the laboratory. Several substances, generally referred to as "interfering substances," will make the specimen unsatisfactory for parasitologic examinations. Urine and water will destroy trophozoites, and feces contaminated with either are not suitable for examination. Specimens collected in bed pans should be checked to be sure they are free of urine. Occasionally, feces are dipped out of toilet bowls and thus mixed with water. Not only does water destroy trophozoites, but there is a danger of coprozoic free-living organisms contaminating the feces and making diagnosis difficult. In addition, feces deposited on soil (as may happen with outpatients) are not satisfactory, since free-living larvae and other contaminants from the soil may cause errors in diagnosis. Certain drugs and compounds will also render the stool specimens unsatisfactory for examination or for detection of organisms. Among these are antidiarrheal compounds, antibiotics, antacids, bismuth, and barium (Juniper, 1962). Specimens for parasitologic diagnosis should be obtained before these compounds are used, otherwise. collection must be delayed until the effects have passed. Specimens should not be collected for 7 to 10 days after barium or bismuth have been given, since crystals and particles of these compounds in the feces will interfere with examination and may destroy trophozoites by their abrasive action. Antibiotics often cause a temporary decrease or absence of organisms in the stools and reliable diagnoses may not be possible for 2 to 3 weeks or more. In addition, stools should not be collected from patients receiving gallbladder dye until about 3 weeks afterwards (McQuay, 1969). Specimens collected in very cold regions should not be allowed to freeze, since freezing and thawing may destroy protozoan cysts and trophozoites (Goldman and Johnson, 1950; Chang, 1955). |