Identification of cysts in stool sample, using trichrome or iron hematoxylin staining (19).
More than one sample is recommended (at least 3 stool samples with two days between each), since the presence of cysts in the stool can be highly irregular, and cysts may not be present until a week after symptoms appear. (14)
Trophozoites break up rapidly in the stool, and should not be relied upon to measure an infection (14).
An Enzyme-Linked Immunosorbent Assay (ELISA) may be used to detect Giardia antigens in the stool, and is commercially available (highly sensitive). (14)
String Test: a patient swallows a capsule with a string attached, and when it is passed into the small intestine, trophozoites stick to the string. The string is then removed and examined for the trophozoites. (19)
A duodenal biopsy may also be useful to detect trophozoite presence, although trophozoites may be hard to distinguish in the sample (14).
Seropositivity tests are not recommended, since they cannot distinguish between current and previous infections (19).
A CBC (complete blood count) is not helpful, because eosinophilia is not present, and the white blood cell count should be normal. (14)
