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Test ID: GIAR Giardia Antigen, Feces

Reporting Name

Giardia Ag, F

Useful For

Sensitive screening for the detection of Giardia antigens present in fecal specimens

Clinical Information

Giardia duodenalis (also known as G lamblia, G intestinalis) is a flagellated protozoan parasite found in contaminated natural streams, lakes, and surface water municipal reservoirs. Humans become infected when ingesting the environmentally resistant cysts in water, food, and by the fecal-oral route.


Giardia infects the small intestine by attaching to the mucosa with a ventral sucking disc. Infection may be associated with a variety of outcomes ranging from asymptomatic disease (estimated to occur in 50% of infected individuals) to acute and chronic giardiasis. When present, symptoms generally appear 7 to 14 days after infection, and consist of watery diarrhea, malaise, malodorous steatorrhea, flatulence, abdominal cramping, nausea or vomiting, weight loss, and low grade fever. Less commonly patients experience constipation and urticaria. Symptoms will resolve in most patients after a period of several weeks. However, approximately 15% to 20% will remain chronically infected without treatment and experience ongoing loose stools, weight loss, malabsorption, steatorrhea, abdominal cramping, flatulence, and burping. Longstanding malabsorption may result in vitamin deficiencies and hypoalbuminemia. Acquired lactose intolerance may also occur, and may persist for months after successful parasite eradication.


Giardiasis is the most common intestinal parasitic infection in the United States that is reported to the CDC and is a common cause of diarrhea in children (especially in day care centers), travelers, and campers or hikers. It is also responsible for waterborne epidemics. Although Giardia parasites (cysts and trophozoites) may be seen using the microscopy-based stool parasitic exam (OAP / Parasitic Examination, Feces), this is an insensitive method for detection and requires examination of three or more specimens. Instead, detection of parasite antigen or DNA is recommended for optimal sensitivity. The Giardia antigen test (GIAR / Giardia Antigen, Feces) is ideal for settings in which giardiasis is specifically suspected (eg  outbreak scenarios), whereas the multiplex gastrointestinal PCR panel (GIP / Gastrointestinal Pathogen Panel, PCR, Feces) is better suited for evaluating multiple potential causes of diarrhea, including parasitic, viral and bacterial pathogens.


See Parasitic Investigation of Stool Specimens Algorithm and Laboratory Testing for Infectious Causes of Diarrhea in Special Instructions for other diagnostic tests that may be of value in evaluating patients with diarrhea.


A positive enzyme-linked immunosorbent assay (ELISA) indicates the presence in a fecal specimen of Giardia antigens.


As per the manufacturer, the assay has a sensitivity of 96%, specificity of 97%, and a positive predictive value of 95%.


Interpretation of results should be correlated with patient symptoms and clinical picture.

Report Available

Same day/1 to 4 days

Day(s) Performed

Monday through Saturday

Clinical Reference

1. Janoff EN, Craft JC, Pickering LK, et al: Diagnosis of Giardia lamblia infections by detection of parasite-specific antigens. J Clin Microbiol 1989;27:431-435

2. Hanson KL, Cartwright CP: Use of an enzyme immunoassay does not eliminate the need to analyze multiple stool specimens for sensitive detection of Giardia lamblia. J Clin Microbiol 2001;39(2):474-477

3. Centers for Disease Control and Prevention: Parasites-Giardia. Accessed 10/16/2019. Available at

Method Name

Enzyme-Linked Immunosorbent Assay (ELISA)

Specimen Type


Ordering Guidance

Duodenal, colonic wash, or small bowel aspirates are not acceptable for this test. If giardiasis is suspected, order test ID, OAP / Parasitic Examination, Feces.

Specimen Required

Submit only 1 of the following specimens:



Specimen Type: Preserved feces

Supplies: Formalin 10% Buffered Neutral (T466); Stool Collection Kit, Random (T635)


Preferred: Fecal container with 10% buffered formalin preservative

Acceptable: SAF (sodium acetate formalin)

Specimen Volume: 5 g

Specimen Stability Information: Ambient (preferred) 60 days



Specimen Type: Unpreserved feces

Supplies: Stool container, Small (Random), 4 oz (T288); Stool Collection Kit, Random (T635)

Container/Tube: Fecal container

Specimen Volume: 5 g

Specimen Stability Information: Frozen 60 days

Specimen Minimum Volume

2 g

Specimen Stability Information

Specimen Type Temperature Time Special Container
Fecal Varies

Reference Values


Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
GIAR Giardia Ag, F 6412-1


Result ID Test Result Name Result LOINC Value
24085 Giardia Ag, F 6412-1

Testing Algorithm

The following algorithms are available in Special Instructions:

-Parasitic Investigation of Stool Specimens Algorithm

-Laboratory Testing for Infectious Causes of Diarrhea

Mayo Clinic Laboratories | Microbiology and Infectious Disease Catalog Additional Information:

mml-travelerinfections, mml-giinfections