Most reputable allergists won't diagnose an initial food allergy without a reaction from eating the food.Not sure that one is true, actually-- the gold standard these days is to not even TEST for something without a good reason (reaction history and suspicion).
BUT, there are still a LOT of allergists out there using skin prick testing and RAST numbers to "diagnose" allergies with no clinical history at all-- and the bad part of that is that the former has about 50% false positives, and the latter isn't much better than that. On the flip side, negative testing is much more likely to be accurate-- about 95% accurate in skin tests, and-- well, it's hard to say with RAST values, but it's at least 75%.
Protein component testing is pretty promising here, actually-- for example, with peanut, there are 8+ seed storage proteins that come up when you run ELISA's (blood tests) for IgE, but only a couple of them are associated with anaphylaxis potential. So someone who skin tests positive for peanuts but has no clinical history, or one suggesting that this might be something more like pollen-allergy-syndrome, that person could now be component tested to see whether Ara h2 lights up or not (that's one of the bad ones).
For more info about that:
https://www.uknowpeanut.com/So it's been known for a long time that about 35-40% of people with peanut allergy have the ability/propensity to anaphylax, but it's only in the past 3-5y that researchers have had ANY idea how to tell who is who there (barring the obvious, of course). It also seems fairly likely that those with some kinds of IgE are less likely to "outgrow" allergies.
Again, this isn't really news, as prominent clinicians in the field have known for a long time, for example, that children who tolerate baked egg or milk (heat denatured) tend to be "outgrowers" and those who don't tend to never outgrow, or to do so quite late.
So again, one of two types of IgE there-- the kind that seems to be sequence-specific, perhaps, or the sort that depends upon native tertiary protein structure.
In short, Ultramarina is ABSOLUTELY correct to state that this is a total quagmire diagnostically. There are far too few GOOD pediatric food allergy specialists out there, and at the other end of the extremes; far, far, FAR too many quacks waving energy wands over people...
