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.

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

These tests are specific for Giardia lamblia and do not test for other intestinal infections that cause similar symptoms. People may get infected with other organisms that cause the same symptoms if they travel 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.