Diagnostic Tests 

• 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)