Differentiating Giardia and Dientamoeba Trophozoites from the Commensal Flagellated Trophs

If using routine microscopic methods to diagnose Giardia, multiple stool samples may need to be examined since cysts are often shed intermittently. Recovering trophozoites is more difficult since they adhere to the mucosa. Therefore, other methods may be more useful such as the string test or duodenal aspirate (see section on other methods of diagnosis).

For Dientamoeba, since only a trophozoite form exists for the most part, it is important to have a fresh stool. Permanently stained slides are recommended instead of direct wet preps because these organisms may be difficult to recognize.

Table 6 shows some means of differentiating the trophozoites of the two pathogens from some of the more common non-pathogens.