Читать книгу Practical Guide to Diagnostic Parasitology - Lynne Shore Garcia - Страница 80

If there are likely to be delays from the time of specimen passage until examination in the laboratory, the use of preservatives is recommended. To preserve protozoan morphology and to prevent the continued development of some helminth eggs and larvae, the stool specimens can be placed in preservative either immediately after passage (by the patient using a collection kit) or once the specimen is received by the laboratory. Several fixatives are available: formalin, sodium acetate-acetic acid-formalin (SAF), Schaudinn’s fluid, polyvinyl alcohol (PVA), and single-vial systems (Table 3.3). Regardless of the fixative selected, use of the appropriate ratio of fixative to stool (3 parts fixative to 1 part stool) and adequate mixing of the specimen and preservative are mandatory. Although many products are commercially available, the most commonly used preservatives are discussed below. They are all available from various scientific supply houses.

When selecting an appropriate fixative, keep in mind that a permanent stained smear is required for a complete examination for parasites. If the physician orders a fecal immunoassay such as FA, EIA, or the rapid-flow method, you will need to confirm that the fixative you are using is compatible with the immunoassay you have selected. It is also important to remember that disposal regulations for compounds containing mercury are becoming more strict; each laboratory will have to check applicable state and federal regulations to help determine fixative options.