Cysts of G. duodenalis (lower right) and Cryptosporidium (upper left) labeled with commercially available immunofluorescent antibodies.

Giardiasis is diagnosed by the identification of cysts or trophozoites in the feces, using direct mounts as well as concentration procedures. Cysts are typically seen in wet mount preparations, while trophozoites are seen in permanent mounts (i.e. trichrome). Repeated samplings may be necessary. In addition, samples of duodenal fluid (e.g., Enterotest) or duodenal biopsy may demonstrate trophozoites. Alternate methods for detection include antigen detection tests by enzyme immunoassays, and detection of parasites by immunofluorescence. Both methods are available in commercial kits.

Direct Immunofluorescence Assay (DFA)

A direct immunofluorescence assay (DFA) is available for diagnosing Giardia duodenalis infections. Antibodies tagged with fluorescent markers are added to stool and incubated. Visualization under a fluorescent microscope shows the Giardia cysts as green, glowing ovoid objects. This test includes antibodies for Cryptosporidium and both diseases can be tested for simultaneously.

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