This qualitative EIA-type test will ordinarily be performed as a substitute for "stool for O & P" unless the clinician is very specific in requesting a microscopic stool exam, or names  parasites other than Giardia or Cryptosporidium as the search target, or the patient is identified as having been in a foreign country. The   specimen is stool/feces from rectum or stool sample (on swab, spatula, plastic spoon, etc.) obtained from diaper or "pottie"/toilet. It is a two-in-one test for the two most common intestinal parasites in the USA. This is an immunological test which detects G. lamblia and Cryptosporidium antigen (Ag). Whereas organisms  are only sporadically present in microscopically recognizable form in fecal stool, "GSA 65" and "CSA" 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 both parasite Ags. 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. Most test will be negative because these parasites have a less than 10% general prevalence in the USA. A positive test means that one or both parasites have parasitized the patient. So, one then uses residual stool specimen to perform similar EIA tests for giardia and cryptosporidium.

Negative, non-reactive, undetectible test status:

• indicates a high probability that the patient does not have either parasite

• 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

Positive test result:

• indicates parasitization by one or both parasites