Problem with those is where you can end up, there are various charlatans around the place. We've one clinic, a big one, well renown and full of utter deceit and snake oil. Anyone entering the building will be found (after expensive tests) to be allergic to a whole variety of gubbins, and sold 'potions' (very expensive) to remove it from their system.
It is run by a medical doctor, and he abuses his title to sell his 'science' upon people.
One anecdotal incident I am aware of, was he diagnosed an elderly woman, terminally ill with cancer (and a family desperate for any way out) with an allergy to selenium. Determined by placing her dentures on her stomach and watching the way her legs rose off the table. Subsequently advised a set of selenium free dentures (which his mate down the road happy makes - expensively) and various potions to get the selenium levels in her body down.
As if this would cure her ills and her cancer.
The immunology doc will know much more on the topic than I do, but there are different immunological responses to different things, and my understanding is just flagging an IgG response to something might not in itself be indicative of an allergy to that substance at that time.
I have considered such testing myself, and frankly I'd love to have a whole raft of hundreds of things tested, just to see and know, but it is cost and actual benefit in believing the results you are given and the knowledge and background to interpret such things.
I previously tried one which requires a small amount of blood mixed with the relevant solutions and nothing was flagged up.
