Antigen tests for giardiasis

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Exam Overview

For a giardia antigen test, a stool sample or fluid from the upper part of the intestines (duodenal fluid) is tested in the lab for the presence of antigens from Giardia lamblia. This test is often done at the same time as stool analysis.

Why It Is Done

An antigen test may be done if a person's medical history and symptoms suggest giardiasis. This test may be done to check if the person has been cured after treatment. An antigen test also may be used to screen people who are at high risk for having giardiasis.

Results

A test that detects Giardia antigens (positive result) indicates that the person has giardiasis. If the infected person does not have symptoms of infection, he or she may be a carrier or have an chronic infection.

These tests are very specific for Giardia lamblia and do not test for other intestinal infections that cause similar symptoms. A person may get infected with other organisms that cause the same symptoms if he or she travels to countries where these organisms are found.

If the test does not detect antigens (negative result), it may need to be repeated to rule out giardiasis.

What To Think About

These tests may be done on a stool sample before testing the fluid from the small intestines (duodenal contents), because getting a stool sample is easier. Antigen tests are very likely to detect Giardia lamblia if it is present and may be used instead of stool analysis when giardiasis is likely. Stool samples may be done to detect antigens (proteins that come from Giardia lamblia) or to detect the actual parasites.

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Credits

Last updated:	October 16, 2007
Author:	Maria G. Essig, MS, ELS
Reviewed By:	E. Gregory Thompson, MD - Internal Medicine, W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
Editors:	Susan Van Houten, RN, BSN, MBA, Pat Truman, MATC