Giardia antigen detection in patients with chronic gastrointestinal disturbances

Giardia lamblia, a protozoan parasite, is transmitted by cysts in contaminated water or food or by person-to-person contact. The standard in diagnosis has been the microscopic demonstration of fecal cysts, which yields many false negatives due to high variability in cyst excretion. A new method that detects infection even when few parasites are present is now available. This immunodiagnostic test is rapid, sensitive, and specific, and typically requires only a single stool specimen. In this study patients with gastrointestinal (GI) complaints were screened for Giardia antigens, and the test results were compared to conventional microscopy. Costs incurred by patients with chronic GI problems were documented.

Twelve patients with GI complaints were tested for Giardia by microscopy and 13 patients by the immunodiagnostic test. Patient charts were evaluated for pertinent history and the diagnostic tests ordered before giardiasis was considered.

For all patients, microscopy was uniformly negative, but 6 of 13 patients were antigen positive. Patients with chronic complaints, later found to test positive for Giardia, typically underwent five diagnostic tests at a cost of $338.

Giardiasis, an increasing problem in family practice, should be considered early in patients with GI disturbances. New, sensitive immunodiagnostic tests that usually require a single specimen are more useful than microscopy. Prompt diagnosis of giardiasis not only relieves patients of unpleasant symptoms, but can avoid unnecessary and costly evaluations.