Who knows a lot about allergy testing?

[Mrs Mungo]

My son was tested for allergies several years ago with the skin prick test. He tested somewhat allergic to trees and a little allergic to dogs. We knew he was probably allergic to birch trees because he used to break out from eating apple and pears. We moved here 2 1/2 years ago. About a year ago he stopped breaking out from eating apples and pears, I thought it might be because he hasn't been exposed to birch in so long?

 

A couple of weeks ago his pulmonologist ran allergy tests again. This time, they did a RAST test. The doctor included panels for trees in the southeast because we are moving back to that are. He didn't test allergic to anything.

 

My question is, if he has not been exposed in the last 3 years, would it even show up on a RAST test?

[Emmy]

Allergy testing is such an enigma. Honestly it may be a very good sign that it didn't show up on his RAST test. Lack of exposure may have caused his body to "forget" the allergy to those things and now the allergy is gone. Of course if you move back to an area where those trees are persistent then he may develop the allergy again (these things are somewhat unpredictable) but hopefully not.

 

Another thing to consider is that the RAST tests aren't as sensitive (IMO) as the skin prick tests.

 

In the end, response to an allergen always trumps allergy testing. So you may not really *know* until he's exposed again.

[Mrs Mungo]

In the end, response to an allergen always trumps allergy testing. So you may not really *know* until he's exposed again.

 

This is my concern. If there is even a CHANCE that he will react again, I'd rather put him on allergy medicine as a precaution. He only has 75% lung function as it is, protecting what lung function he has is a priority.

[ChristusG]

From what I've gathered, allergy testing is kind of unreliable. I had a RAST test done, as well as a skin prick test. I showed an allergy to bananas on the skin prick test. I've had an oral reaction to bananas so I know that was true. However, the skin prick test also showed that I have an allergy to things like soy, eggs, mustard seeds, sesame seeds....I've never shown a reaction to those things. I asked the allergist about it. Basically, he said that if you took a person who has shown absolutely no allergic reactions to anything and gave them the skin prick test, they would test positive for a reaction to 10 or 15 things....even though they do not show reactions to those things. I was like Huh?? I'm not sure of the point of allergy testing. I still don't know what I should steer clear of besides bananas LOL. I carry an epi pen.

[Murmer]

I would say if you are super concerned have them scratch test and then compare the tests. I know my dd was scratch tested then RAST tested and when both where positive we got an epi-pen. So if the scratch responds then I would do meds just in case. If both are negative then I would give it a try. Good luck! I am dealing with my dd and her allergies too (she had hives today no idea what caused them).

[Melissa in Australia]

the skin prick test is only testing for a histamine reaction. My husband has chemical sensitivities, he is allergic to a huge amount of things, including pine trees. this does NOT show up in skin prick tests, he had to have drops under the tongue tests. He doesn't have a histamine reaction.

Edited July 15, 2010 by melissaL

[AuntieM]

I would not rely on the RAST test. I guess I would say that I would trust it for a positive, but not for a negative, kwim?

 

This is a toughie, though. DS, on a skin prick test, will show positive to things to which he does not actually react.

 

Seems like the only way to know for sure is to see if he actually reacts once you're there. But I sure do understand your reluctance to do that.

 

I am curious about the under-the-tongue drops... no experience there. Perhaps it's something to ask about?

[Amber in AUS]

When we have done allergy testing here it has been skin scratch/prick testing followed by RAST blood testing to further identify allergens. Given you sons other medical issues i would be asking for a follow up skin scratch/prick test and then if there is no reaction go with it.

 

Children can grow out of very serious allergies when the allergen has been removed from their environment for an extended period. This is obviously a minority, i am just saying that it is possible. Both of my nephews who were anaphylactic to all tree nuts as small children are now allergy free as teenagers.

[Mom in High Heels]

I would not trust the RAST test. I have allergies to a billion things (at least it feels that way) and half of them don't show on the RAST. The skin prick test is often a better indicator, though it does show things that you may not react to as allergies. My doc said that means you are technically allergic, but you don't react in a typical fashion. He said it can just keep your body in a sensitive state and make your reactive allergies worse. Most of my non-reactive allergens are foods. I do have foods I react to (all oral allergies that make my lips swell or the back of my throat itch like mad), but there are several that I show no reaction to. I have found that if I cut those foods out of my diet though, my reactions do seem to be less.

Children can grow out of allergies (I out grew many-thank goodness), so it is possible that he is no longer allergic to birch, but the only way to know for sure is a prick test or exposure.

Best of luck to you and your son. Allergies are so difficult to live with.

[AuntieM]

Mrs M, have you discussed immunotherapy with his pulmonologist? Is he a candidate for it? It worked so very well for my ds... I always suggest one consider it when allergies are severe.

[sbgrace]

I think some people are more accurate with skin prick (my son) and others with RAST (a friend's son). Generally allergy testing is more accurate for environmentals compared to foods in my understanding. For foods you have a 50% false positive rate (false negatives much less likely though possible). Environmental allergies are more accurate in that if you get a positive you are likely allergic in my understanding.

 

My son's allergist does skin prick and follows up with RAST to confirm or get number indicators for serious allergies.

 

He could certainly "lose" an allergy without exposure. That's the whole idea of outgrowing food allergies after all! I hope it stays negative for him.

[Mrs Mungo]

Thanks, everyone. I think it probably is best to wait until we get back to the mainland, see how things go and have him tested again after we've been there a while.

[TravelingChris]

My youngest is most definitely higly allergic to wasps. She has had an anaphalactic reaction to a sting, had the start of an anaphalactic reaction to an allergy shot once when they were titering up, and had positive skin and RAST tests to it. This year, we skin tested her for other insects and it showed positive for bees, hornets, etc. THe doctor ordered a RAST test, and now it all came back negative. Yet she had such a bad delayed reaction to the skin testing that we had to miss a field trip, get back over to the allergists office, and have her go on big doses of prednisone for three days. Is she allergic to these things, you betcha. SO was my mother. I have never been stung by any wasp, hornet or bee so I don't know if I am too. Neither have my other two kids.