Positive Skin & Negative CAP RAST


Has anyone ever had a positive skin test and negative CAP RAST? This is the case with my son's almond test. What does this mean? Is he allergic or not?

On Aug 23, 2001

No, but this is what I'm hoping for. I'm taking Ben for a CAP RAST on Oct 2. His skin prick test was very positive (4++) but he has never reacted, and he has been exposed. So I'm hoping the CAP RAST is negative. If so I would think the next step would be oral challenge. I once heard that a skin prick test can take up to 7 years to clear after an allergy is outgrown, but recently heard that it can last a lifetime.

Has your child ever reacted to almonds? I would talk to your allergist about an oral challenge.

On Aug 24, 2001

I had the same situation with my daughter her skin test both times she was tested for peanuts was positive but her rast test was negative. The allergist at Children's said that this is still an indicator that she is allergic to peanuts and treat her accordingly. I also talked to the allergy nurse who said she sees that fairly often and when some of these kids have been oral challenged they react. Hope this helps-Of course it is probably best to talk with your child's doctor. Cheri

On Aug 26, 2001

Same with Nicholas. His RAST came out negative, but the doctor said to wait a year for another RAST. If it's negative then a skin prick test followed by an oral challenge. He said it is not uncommon to react even with a negative RAST. This did not make me happy! But next year he will be 5, and another negative RAST could mean a possible outgrowth of this allergy.

On Aug 27, 2001

My son has never reacted to almonds before. He ate Honey Nut Cheerios all the time before we knew of his PA. He accidentally ate an almond at my MIL's house the end of June and didn't react. I spoke with the allergist on Friday AM and he said it could either be the skin test was false positive or my son's almond IGE is so low that the CAP RAST isn't detecting it. Either way, I have to treat him as though he is allergic and we can do another skin test next year.

On Aug 27, 2001

This is the most frustrating part of food allergy to me. I've been told that if you eat it and don't react, you aren't allergic. It seems to me that being able to eat a food is more proof than a skin prick test, but what is really going on with the skin test then? Something's not right. I've also been told a positive skin test can last your whole life even if you outgrow the allergy. I get so frustrated with these tests and wish someone would come up with something unequivocal. As far as I know, the CAP RAST is the best for determining likelihood of a reaction. I think your son isn't allergic to almonds. Now, because of cross-contamination issues, I wouldn't give them to him anyway, but it would still be nice to know. It's so frustrating.

On Aug 28, 2001

My son has had reactions, tested positive with the skin test, but was negative with the RAST test. Since it had been about 18 months since his last reactions and he was 5 (usually the age they say they will outgrow their allergies if they are going to) we did an oral food challenge. I posted a thread awhile back on our experience with this.....which was a bad one.....but he did test positive with the oral challenge. When he vomited, he vomited in his left hand, wiped his mouth with his right hand and immediately broke out in hives in the areas of his skin that had vomit. After only a couple of minutes, the hives spread, he was itching like crazy and he was complaining aobut his throat. He even had hives under a sock where two drops of vomit had landed! Luckily we were in a hospital and he was ok after some Benadryl, but it proved the RAST test isn't always reliable. The doctor explained that they do get cases where children have negative RAST, but still test positive with the oral challenge. The doctor wants to retest when he's 8 (he's 6 now), but I'm not sure we're going to. He also wanted to oral challenge the two tree nuts his skin tests were positive for, but were negative with the RAST, but I said absolutely not. Without going into a lot of history, I think the only way I would even consider another oral challenge is if he tested negative with a skin contact test first. Meaning....they put peanut butter on his skin with no reaction. I will never make my child eat something like that again!

On Sep 1, 2001

My Allergist just told me that a skin test is way more sensitive than the rast test. (I thought it would be the other way around!) My son's rast showed 0 for shelfish but when we re-tested him with the skin test he was a 4 plus for shrimp . He said this meant he was still allergic to shrimp.