Positive Skin Test, Negative RAST


Hi All, Last summer my son (who is 2) tested 4+ for peanuts on the skin test and last week he had the RAST test done and that came out negative. Has this ever happened to anyone? Is it possbile he outgrew the allergy? The Dr. said he would like to do an oral challenge at the hospital. If you have heard of this could you please let me know your experience, thoughts, ideas. Thanks.


On Mar 7, 2005

Hi: My son is PA. So we had our DD tested and she had a positve skin test 3 times and then we did a RAST and it was negative. We were also told to do a taste challenge. We booked an app. , and had to cancell because of an ice storm, next app. she was sick. So I snuck a tiny amount of pp into the house while my DS was at school and had her try it (with 2 epi pens, on the table, just incase). She was okay with it so I gave her more and she was okay, no hives or anything. She has never reacted to peanuts, in the past it was just to know for sure, in preparation for school in the fall. I would not have done this had she had any kind of reaction in the past. My DH and I thought she was not allergic, she did not have the eczema as a baby as our other 2 did and have allergies, usually that is a sure indicator of allergies. We were told that skin test is more accurate than a RAST, but past history is a better indicator. Good Luck to you.

On Mar 7, 2005

sherkelsey, when I had my daughter tested for PA (skin prick) when she was 3, just so I would know before she went to school, I also decided to have her brother "officially" tested (also skin prick). He definitely came back PA, but he also came back with a LONG list of false positives, which I didn't understand. I posted about it here and found out that yes, false positives do happen.

I know that if I were to have either child tested again it would be the RAST test as I understand it is more reliable.

To me, it sounds as though the skin prick may have been a false positive.

If I were you, I would go for the oral challenge at the hospital. It really does sound as though your child isn't PA.

Best wishes! [img]http://uumor.pair.com/nutalle2/peanutallergy/smile.gif[/img]

On Mar 7, 2005

Last summer before he was skin tested he did react on 3 separate occassions to Peanut, (hives on face). Do you think I should have his RAST test redone and another skin test before going ahead with the oral challenge?

On Mar 7, 2005

Has your child ever had an anaphylactic reaction?

Also, I have never done much research re skin prick versus RAST testing, just understand from reading here that the RAST is considered better, but wondering if that is a question to ask - can you get a false positive or negative on a RAST test?

Not clear if the question has been asked, but perhaps you'd like to raise that one separately to see what response you do get from people that have had their children allergy tested.

I've just always known my guy was PA, so even when he was skin prick tested, I wouldn't allow them to scratch where they were putting the peanut serum - he reacted with a huge wheal just by having the serum placed on his skin regardless and that was enough for his allergist to say that yes, he was definitely PA.

But there are people here with definitely a lot more experience re allergy testing than I have, since I consider mine to be basically nil.

Sorry not to be much help.

I definitely would not do an oral challenge at home though, especially if your child did react just last summer.

Best wishes! [img]http://uumor.pair.com/nutalle2/peanutallergy/smile.gif[/img]

On Mar 8, 2005

I just had my son in at the pediatrician today and she has a 4 year old son with peanut and egg allergies. I got to talking about my daughter's allergies and she mentioned her son tested negative to eggs on the CAP RAST test but skin tests are positive. She and their allergist believe he is contact allergic but he does react with face puffiness, etc. She is sure he is allergic. I didn't talk to her in-depth about it but your post reminded me of our conversation today.

I hope your child is not allergic because I have heard skin tests can take years to become negative even though the allergy is outgrown.

On Mar 8, 2005

I don't think it would hurt to redu both test prior to a challange, but that is M/O

On Mar 8, 2005

My son has had false negative RAST results for several foods, including peanut.

Please do not considere an oral challenge unless the RAST is repeated. Also please look into the difference between RAST and CapRAST, which is supposedly more reliable.

There is a member here whose child underwent an oral challenge with a negative blood test. She reacted severely and needed multiple Epi's.

I don't mean to be pessimistic, but with several reactions occuring less than a year ago, I would think it improbable that your child had outgrown the allergy so quickly.

Hoping for good news for you.

On Mar 8, 2005


Thanks so much for your response. When your son's results came back negative, what did you and the Dr. do as the next step(did they do further blood tests, skin pricks)? How was it determined that they were false negatives?