Other tests may be done to help your doctor detect giardiasis or other organisms that may be causing long-term symptoms, especially if problems with malabsorption are occurring.

An upper gastrointestinal (UGI) series or a biopsy of the duodenum often is not specific enough to help in diagnosing giardiasis. But a biopsy may reveal organisms other than Giardia lamblia, such as cryptosporidium or microsporidium, or the presence of a condition such as celiac sprue.

The doctor may collect a sample of fluid or tissue from the duodenum if:

• A person has low levels of immune proteins in the blood (hypogammaglobulinemia).
• A person has AIDS and chronic diarrhea, but Giardia lamblia or other parasites are not found in the stool analysis.
• A person has long-term diarrhea, but prior tests have not determined a cause.
• Multiple diseases or causes are being considered, and more tests will help clarify the diagnosis.