PERMANENT STAINED SMEAR: Introduction (cont.)

recommended for every stool sample submitted for a routine parasite examination (mandatory part of the O&P examination).

There are a number of staining techniques available; selection of a particular method may depend on the degree of difficulty of the procedure and the amount of time necessary to complete the stain. The older classical method is the long Heidenhain iron hematoxylin method; however, for routine diagnostic work, most laboratories select one of the shorter procedures, such as the trichrome method or one of the modified methods using iron hematoxylin.

Most problems encountered in the staining of protozoan trophozoites and cysts in fecal smears occur because the specimen is too old, the smears are too dense, the smears are allowed to dry before fixation, or fixation is inadequate. There is variability in fixation in that immature