If corn allergy has produced gi symptoms will an allergy test confirm or will it not likely show up? and is it worth it to do an allergy test?

Go to an allergist: Allergy to corn is no common, but can be severe. The tests for allergy to corn are not reliable. If an allergy specialist feels it is required the only proof of corn allergy would be in oral challenge.But this should be performed under the guidance of an allergist trained in doing food challenges.

Food allergy test : It depends on what GI diseases you are suspected to have and what type of allergy test you use - prick or patch test. Some GI conditions are ige mediated, some by immune cells and some mediated by both processes. Ige mediated conditions tend to be more obvious and explosive like rashes, anaphylaxis while immune cell mediated process is more insidious like abdominal pain, blood in stool.