We waited a while to introduce our oldest to peanut butter, my wife was pretty scared about it because she had a friend growing up with a peanut allergy. It just kinda got to the point where we didn't have peanut butter in the house anyway, it just wasn't a staple, not out of any real thought to specifically avoid it.
There is no history of food allergies in either family, though my side does have some heavy animal allergies. We finally gave him a spoonful of peanut butter and he broke out in hives and then threw up about 10 minutes later. We freaked out of course and had him in for some allergy testing, he had a pretty big blow up with the skin prick test and his blood levels came back very high.
This is where everything gets to be an approximation. We still don't know his allergy. A skin prick test just proves that the allergens on his skin react to it. The blood test proves he has the potential for a big reaction to peanut proteins in him. Apparently there are 8 proteins in peanuts, and some cause stronger reactions than others. It is possible your blood test comes back 'high' yet your body doesn't react to the proteins that will cause an anaphylaxis reaction.
Further, it depends how your body breaks down the protein in your digestive system, it could be possible to come back with high levels on the test yet your body breaks everything down into small enough quantities that the allergen never triggers even though you have the potential for an explosive reaction.
The only authoritative way to determine the allergy is an oral challenge, but due to our son's high levels and his previous reaction, would be really dangerous for him until he is a bit older. The only thing to do is keep testing and hoping the levels drop enough to try a challenge.
Right now hes in 'avoid cross contamination' mode and it really is a bit life changing. We have to take an epi pen around with us and be 'those people' that ruin it for everybody. My son has to ask if new food is safe, because we put peanuts in every god damn product. We had a sunblock we put on him that caused him to break out in a rash and we looked up the ingredients and one of them was derrived from peanuts. It is insane.
And nobody gets it, even here some of the comments are really insensitive because they love their peanut butter. For us that substance is a deadly poison that targets our son and it is everywhere, every, fucking, where. I've been on there other side where I've gotten on a plane and couldn't eat the snack I brought with me and complained, but I guess once I get on the other side of it, I realize how scary it can be.
We were playing at a rec center after a group class and he was making new friends playing at a pool table when I noticed a dad come over with a half eaten sandwich to give to his kid... whats on the sandwich... peanut butter! SHIT they've all been at the same table touching the stuff, that kid is little he'll be all over with that food, we have to GET OUT OF HERE NOW.
That is the bullshit you have to deal with with this thing, the world is suddenly full of boobytraps that'll put your kid in the hospital or kill him if you aren't fast enough to stick him with the epi pen. It SUCKS, way more than having to wait to eat my snack until after I got off the plane.