Antigen tests for giardiasis

Exam Overview

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

Why It Is Done

The antigen tests are used if the person has a medical history and symptoms that suggest giardiasis. They may be done to check that the person has been cured after treatment and may also be used as a screening test.

Results

A test that detects antigens (positive result) indicates that the person is infected with G. lamblia. If the infected person does not have symptoms of infection, he or she may be a carrier or have an inactive chronic infection.

These tests are very specific for Giardia lamblia. If the symptoms are caused by other intestinal infections, giardia antigen tests will not detect those other organisms. This may be a factor if the person has traveled to places where he or she may have been exposed to other organisms that could cause the same symptoms.

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 performed on a stool sample before the fluid from the small intestines (duodenal contents) is sampled, because obtaining a stool sample is not as time-consuming. Antigen tests are very likely to detect Giardia lamblia if it is present and may be used instead of stool analysis in situations when giardiasis is strongly suspected. Stool samples may be done to detect antigens (proteins that come from Giardia lamblia) or to detect the actual parasites.

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Author:	Colleen Cronin	Last Updated October 19, 2005
Medical Review:	Adam Husney, MD - Family Medicine W. David Colby, MSc, MD, FRCPC - Infectious Disease
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