Interpretive Handbook

Test 80231 :
Giardia Antigen, Feces

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Giardia lamblia are flagellated protozoa which can be found contaminating natural streams, lakes, and surface water municipal reservoirs. The human host ingests them in water, food, and by the fecal-oral route.


Giardia infect primarily the small intestine causing diarrhea by unknown mechanisms after attaching by their ventral sucker. Malabsorption may also occur.


Giardiasis is the most common intestinal parasitic infection in the United States and is a common cause of diarrhea in children (especially in day care centers), travelers, and in waterborne epidermics.

Useful For Suggests clinical disorders or settings where the test may be helpful

Screening for the detection of Giardia antigens present in stool specimens.


See Parasitic Investigation of Stool Specimens Algorithm in Special Instructions for other diagnostic tests that may be of value in evaluating patients with diarrhea.

Interpretation Provides information to assist in interpretation of the test results

A positive enzyme-linked immunosorbent assay (ELISA) indicates the presence in a stool specimen of Giardia lamblia antigens.


The assay has a sensitivity of 96%, specificity of 97%, and a positive predictive value of 95%.


Interpretation of results should be correlated with patient symptoms and clinical picture.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Small numbers of Giardia residing only in the duodenum may not yield a positive enzyme-linked immunosorbent assay (ELISA).


Giardia antigen detection should be used as an aid in diagnosis of giardiasis. A single diagnostic assay should not be used as the only criteria to form a clinical conclusion.


Testing of 3 consecutive stool specimens is recommended before considering the results negative.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


Clinical References Provides recommendations for further in-depth reading of a clinical nature

Janoff EN, Craft JC, Pickering LK, et al: Diagnosis of Giardia lamblia infections by detection of parasite-specific antigens. J Clin Microbiol 1989;27:431-435