aEntamoeba histolytica is being used to designate the true pathogenic species, while E. dispar is now being used to designate the nonpathogenic species. However, unless trophozoites containing ingested red blood cells (E. histolytica) are seen, the two organisms cannot be differentiated on the basis of morphology in the permanent stained smear. Fecal immunoassays are available for detecting the Entamoeba histolytica/E. dispar group or for differentiating the two species.
Table 2.3 Body sites and possible parasites recovered (trophozoites, cysts, oocysts, spores, adults, larvae, eggs, amastigotes, and trypomastigotes)a
SECTION 3
Collection Options
Various collection methods are available for specimens suspected of containing parasites or parasitic elements (Table 3.1). The decision on the method used should be based on a thorough understanding of the value and limitations of each. The final laboratory results are based on parasite recovery and identification and will depend on the initial handling of the organisms. Unless the appropriate specimens are properly collected and processed, these infections may not be detected. Therefore, specimen rejection criteria have become much more important for all diagnostic microbiology procedures. Diagnostic laboratory results based on improperly collected specimens may require inappropriate expenditures of time and supplies and may also mislead the physician. As a part of any continuous quality improvement program for the laboratory, the generation of test results must begin with stringent criteria for specimen acceptance or rejection.
Clinically relevant testing also depends on the receipt of appropriate test orders from the physician (Table 3.2). The laboratory is not authorized to order tests; this function is the responsibility of the physician. Depending on the patient’s history, very specific diagnostic tests are recommended. It is very important that physician clients become familiar with the test order options available from the laboratory testing menu. They must also have an understanding of the pros and cons of each test when considered within the context of the patient’s symptoms and clinical history. Without the appropriate test orders and collection 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