Can the fecal immunoassays be used for duodenal fluid (giardiasis)?
First of all, the tests have not been approved/validated for this type of specimen. Also, the duodenal fluid/aspirate would contain primarily the trophozoite form, not the cyst stage for which the reagents have been designed. An example: if one is using the FA (rather than EIA or cartridge) the trophs may appear to be fluorescent at a very pale 1+, while the cysts are a strong 3-4+. So, while there may be a few antigenic sites that are shared by the cysts and trophs, the commercial tests for Giardia are picking up the cyst antigens. You can “try” the reagents on these specimens, but if the result is negative, the result in no way has “ruled giardiasis out.” I would just recommend testing stool; this approach might avoid the need for duodenal aspirate testing altogether.
