This specific qualitative EIA-type (ELISA) test will ordinarily be performed when the GLCS screening test is positive. The   specimen is (left-over specimen from the GLCS test can be used) stool/feces from rectum or stool sample (on swab, spatula, plastic spoon, etc.) obtained from diaper or "pottie"/toilet. This is an immunological test which detects G. lamblia antigen (Ag). Whereas organisms (populating the duodenum and small bowel lining-cell surfaces) are only sporadically present in microscopically recognizable form in fecal stool, "GSA 65" antigen (Ag) is nearly constantly present in the parasitized patient's feces. So, this is a much better test than stool "wet prep exam" or "stool for O & P". It does not cross-react with antigen from other parasites, and it is stable during routine conditions of specimen acquisition, transport and storage.

Test wells are reagently coated with monoclonal Ab against the parasite Ag. As test sample is exposed to the test-well surface, the attached monoclonal Ab "captures" parasite Ag from the stool (if any be present), forming an immobilized Ag-Ab complex on the well surface. The test well is incubated and then  washed to get rid of any excess unbound Ag. A reagent enzyme conjugate (monoclonal anti-Ag "labled" with the enzyme horseradish peroxidase) is then added to the test well and the conjugate complex "sticks" to any Ag-Ab complexes lining the well surface (if any be present). Then any excess is washed from the well. The colorless substrate for the enzyme lable to react on, TMB, is then added. If any enzyme be attached to the well (onto Ag-Ab complexes), then the TMB "triggers" and turns into a yellow-colored reaction product which can be detected visually or with an spectrophotometer. Test controls are always used to make sure that all components are working.

Giardiasis causes an estimated 2,000,000 infections per year in the USA. Is a fecally contaminated mode of infection and may thereby include co-infections with other feeces-transferred agents.

Negative, non-reactive, undetectible test status:

• indicates a high probability that the patient does not have giardiasis

• it is theoretically possible to have such a light parasitization (or to test an incompletely treated case with a very light residual population) and have a "false negative" test result; if necessary, a duodenal aspirate can be obtained endoscopically and tested with this ELISA test

• though treatment is standard and cure is presumed if symptoms have subsided, one can test stool greater than 7 days after conclusion of treatment and expect a case "cure" to produce a negative ELISA test

Positive test result:

• indicates G. lamblia parasitization