Giardiasis laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Yazan Daaboul, M.D.; Serge Korjian M.D.

The diagnosis of giardiasis requires the detection of Giardia in at least 1 out of 3 stool samples upon ova and parasite examination. Multiple stool collections (i.e., three stool specimens collected on separate days) should be performed for ova and parasite examination (O & P) to increase test sensitivity since Giardia cysts are excreted intermittently (detection of apprroximately 80% of cases). Blood samples are usually unremarkable. Fecal immunoassays may also be used for the diagnosis of Giardia if stool collections were negative and giardiasis is still suspected. Only molecular testing, such as polymerase chain reaction techniques, can be used to identify the subtypes of Giardia. Blood samples are usually unremarkable.

Blood samples are usually unremarkable. Blood test findings may include the following:

• Eosinophilia (uncommon)
• Elevated anti-Giardia IgM and IgG may distinguish between acute giardiasis (elevated IgM) vs. past infections (elevated IgG)

• Multiple stool collections (i.e., three stool specimens collected on separate days) should be performed for ova and parasite examination (O & P) to increase test sensitivity since Giardia cysts are excreted intermittently (detection of apprroximately 80% of cases).
• Fecal immunoassays may also be used for the diagnosis of Giardia if at least 3 stool collections showed a negative O & P exam and giardiasis is still suspected. Fecal immunoassays are more sensitive and specific than the concentration method and trichrome staining.
• Rapid immune-chromatographic cartridge assays also are available, but should not be ca replacement of the ova and parasite examination.
• Stool culture is not routinely performed due to difficult culturing of the parasite.

• Only molecular testing, such as polymerase chain reaction techniques, can be used to identify the subtypes of Giardia.

Under a normal compound light microscope, Giardia often looks like a “clown face,” with two nuclei outlined by adhesive discs above dark median bodies that form the “mouth.” Cysts have four nuclei.

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