GIAR - Clinical: Giardia Antigen, Feces

Test Catalog

Test Name

Test ID: GIAR    
Giardia Antigen, Feces

Useful For Suggests clinical disorders or settings where the test may be helpful

Sensitive screening for the detection of Giardia lamblia antigens present in stool specimens

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

The following algorithms are available in Special Instructions:

-Parasitic Investigation of Stool Specimens Algorithm

-Laboratory Testing for Infectious Causes of Diarrhea

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Giardia lamblia (also known as G duodenalis, G intestinalis) are flagellated protozoa that can be 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.


G lamblia primarily infects the small intestine causing malodorous watery diarrhea and flatulence after attaching by their ventral sucker. Malabsorption and lactose intolerance may also occur.


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. It is also responsible for waterborne epidemics. Although G lamblia may be detected using the microscopy-based stool parasitic exam (OAP / Parasitic Examination), up to 7 specimens may be necessary for optimal sensitivity. Instead, this test detects antigen using an enzyme-linked immunosorbent assay (ELISA), which is a more sensitive method for detection and is, therefore, a preferred method for detection.


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.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Interpretation Provides information to assist in interpretation of the test results

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

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Small numbers of organisms residing only in the duodenum may not yield a positive test result.


Giardia lamblia antigen detection should be used as an aid in diagnosis of giardiasis. A single diagnostic assay should not be used as the only criteria to form a clinical conclusion.


Testing of at least 2 consecutive stool specimens by enzyme-linked immunosorbent assay (ELISA) is recommended before considering the results negative.


Stool containing large amounts of leukocytes or red blood cells may give falsely positive results.

Clinical Reference Recommendations for in-depth reading of a clinical nature

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

Special Instructions and Forms Library of PDFs including pertinent information and consent forms, specimen collection and preparation information, test algorithms, and other information pertinent to test