Chapter 4 : Specimen Test Options: Routine Diagnostic Methods and Body Sites

Abstract:

This section focuses on ova and parasite examination of stool specimens using routine diagnostic methods and body sites. Diagnostic parasitology includes laboratory procedures that are designed to detect organisms within clinical specimens by using morphologic criteria and visual identification, rather than culture, biochemical tests, and/ or physical growth characteristics. The most common specimen submitted to the diagnostic laboratory is the stool specimen. The most commonly performed procedure in parasitology is the ova and parasite examination (O&P exam), which consists of three separate protocols: the direct wet mount, the concentration, and the permanent stained smear. Several other diagnostic techniques are available for the recovery and identification of parasitic organisms from the intestinal tract. A roundworm parasite that has worldwide distribution and is commonly found in children is Enterobius vermicularis, known as pinworm or seatworm. Diagnosis of pinworm infection is usually based on the recovery of typical eggs, which are described as thick-shelled, football-shaped eggs with one slightly flattened side. Most routine clinical laboratories do not have the animal care facilities necessary to provide animal inoculation capabilities for the diagnosis of parasitic infections. In certain parasitic infections, the standard diagnostic laboratory procedures may not be sufficient to confirm infection or specimen collection may not be practical or cost-effective. In these circumstances, alternative methods may be helpful; these include antibody, antigen, and nucleic acid detection. In the absence of reliable serologic diagnostic tests, skin tests have been used to provide indirect evidence of infection.