Conflicting test results - RAST vs. skin. Thoughts???

Posted on: Fri, 03/09/2001 - 11:53pm
Emily in Maryland's picture
Joined: 08/23/2000 - 09:00

pHello everyone. My son skin tested positive for peanuts at 15 months with a BIG 4+. He also tested negative that time to milk and soy - both of which he reacts to. At 22 months, we took him for a RAST test. He tested negative to everything. He has never been exposed directly to peanuts although he had plenty of prenatal exposure and in the first two months before I eliminated it from my diet. The allergist recommends we continue to be diligent in avoiding peanuts and nuts and continue to always carry the EpiPen - which I strongly agree with. But what could these conflicting tests mean? I know both are known to be faulty. I am very hopeful that this is a sign he may outgrow the peanut allergy. I have no interest in exposing him anytime soon, especially when he's so young and can't tell us how he's really feeling. So, anyone have ideas about how to interpret this?/p
pThanks!br /
Emily, mom to Corey Andrew, age 22 months/p

Posted on: Sat, 03/10/2001 - 12:55am
BENSMOM's picture
Joined: 05/20/2000 - 09:00

Emily, my son tested 4+ for peanuts too. He has never reacted. I would like to get a RAST test on him to see how that turns out. As you said, both tests can be faulty. I, too, live in Maryland, and when I tried to get a RAST test done, the doctor told me that the only reliable lab is the one at Johns Hopkins. I didn't get the test at that time because I had a problem trying to get them to send the blood work to Hopkins.
Anyway, there are a few possibilities. The RAST test could be wrong. Since the doctor told me he only trusts Hopkins to do it "right", maybe it's a tricky test to do. Also, peanuts can cross-react with other things (I was told grass) so maybe he's allergic to something else, and that's what the skin test reaction was. 50% of people with a positive skin test don't react to the allergen. I'm not sure what to tell you. I'm hoping for a negative blood test, and then I'd be in the same boat and don't know what I'd do either. I think I'm going to take Ben to see Dr. Robert Wood at Johns Hopkins. He's supposed to be the best around here and is one of the leading researchers on PA. I want to get a blood test on Ben, and if it conflicts with the skin test, I'd be interested to know what he says.
Sorry I couldn't really help. You just have to keep assuming he's allergic I guess, and hope for a negative skin test when he's older. Since he's never been directly exposed to peanuts, you don't know if he would react.

Posted on: Sat, 03/10/2001 - 6:40am
Helen's picture
Joined: 05/05/2000 - 09:00

I find the lack of defnitive answers one of the most frustrating aspects of allergies. I have no answers but can completely sympathize. My child tested "very high" on the RAST, then negative on a skin test, redid the RAST, again "very high" redid the skin test with a different peanut preparation and this time he did react. His "reactions" were also not clear cut. So . . . although I've resigned myself that he is allergic I sometimes wonder. . .

Posted on: Sat, 03/10/2001 - 1:27pm
Anonymous's picture
Anonymous (not verified)

Emily in Maryland, I'm not sure that I'm going to be any help at all. I would like to say that I completely understand what you're going through. When I took both of my children to the allergist at the end of October, it seemed like I had a wealth of questions (and therefore thread starters for this board) because things are SO confusing.
As far as I can understand it, and it is only from other people posting on this board, certainly not the allergist or a family doctor along the way, the skin test could have been a false positive whereas the RAST test is more reliable.
Does your son have ezcema that could have affected his skin test? When my PA son came back with 5 new allergies, it turned out that he had false positives because he has ezcema on his back where the tests were done.
I know that it's probably something you have to wait for your child to be older to do, but this sounds like one of the rare instances where I would even suggest an oral challenge.
Since I definitely know my child is PA from his three reactions, I know I don't have to do an oral challenge.
However, if you're going to keep getting confusing results from both skin prick testing and RAST tests, then perhaps that is something to consider.
My concern is that your son may actually not be PA. Although I hate peanut products because of what they are capable of doing to my son, I would hate to see someone extremely limiting their diet (especially when you consider all the "may contains" and "made ins") if they weren't really PA. Do you know what I mean?
I also think this may be of more concern when your child is ready to enter the school system. How can you have a 504 Plan for him, if you even want one, if you're not clear if he is PA or not?
I think what your allergist told you was very important - that you still avoid peanut and tree nut products (simply because of your son's age) and to carry your Epi-pen (better safe than sorry), but I do think I would be investigating the pros and cons of an oral challenge for him in the future.
I hope I've been of some help, although I'm really not in the best position because I know my son is definitely PA, without him ever being tested for it.
Best wishes! [img][/img]

Posted on: Sun, 03/11/2001 - 10:17am
AmyR's picture
Joined: 09/26/2000 - 09:00

Have you thought of having another skin test? I had a situation with my daughter a few weeks ago. She is not PA. We had her tested for environmental allergens and the nurse got confused with the order of testing so we couldn't rely on the results. From that skin test, it looked like she was allergic to one of three things (dust mites, mold or dog). We weren't positive which allergen she reacted to so we retested two weeks ago. This time she reacted to all three. We're not really sure what to believe at this point. I realize that PA is a lot more serious so it is a harder call for you. If my PA son had the same results your facing, I'm not sure what I would do either.
I'm sure I wasn't much help but I just wanted you to know that in addition to the tests not always being 100% accurate, the professional can also mess up. Good luck.

Posted on: Sun, 03/11/2001 - 11:57am
jhi's picture
Joined: 03/09/2001 - 09:00

My 5 yr. old daughter has also had conflicting test results, but has a history of hive reactions (face and chest) after eating peanuts. Her first skin test was kind of negative, but was accompanied by sudden itching and a delayed reaction which the allergist didn't get to see. At this point, our allergist prescribed an epi-pen and recommended that we treat it like a PA and then retest in a year. Her second set of skin tests - a delayed reaction again, which the doctor didn't get to see. Her third set of tests: Rast - negative and a positive skin test!!
So, where are we at? We consider that our daughter has a severe PA. We will get her assessed again, but want to get a second opinion at a special allergy centre. I am very worried that if a future set of tests come up negative, she will be deemed non-PA, despite her history of delayed reactions.
There is nothing that I want more than to have her not allergic to peanuts, but I want to make sure that the doctors making this decision are considering her unusual history.
Sorry to not offer any solutions, but I thought you may be interested in my situation.

Posted on: Fri, 03/16/2001 - 4:17am
4jesters's picture
Joined: 03/16/2001 - 09:00

Skin tests do pose a risk, as you can react to the allergen. We are talking intradermal, right?
As for RAST, it is safe, although there is alwayss a possibility of a "false negative." If it comes back positive, it's positive, but if it comes back negative, it could be error.
My son tested positive to 40 foods. Nothing was lower than a 2+. Peanut, egg, soy were 5+. Whey, casein, corn, peas were 4+, and wheat, rye, barley, beef were 3+. Rice, oats, apples, pears, pork, sweet potatoes, carrots, bananas, peaches were 2+. I can't remember the rest.
What does he eat? Well, he can tolerate some things if I rotate them, and, I don't want to bring up controversial issues, but, were are taking him to a Dr. that uses BioSET (branch off of NAET) to treat allergies. We have experienced great success so far. He has been to see her about 10 times since Sept., 2000 and can eat wheat products and dairy products now. He is starting to eat corn products as well.
Mainly, it's yogurt, applesauce, Cheerios, bananas, pears, sausage, bacon, ham, chicken, beef, carrots, potatoes, rice, grapes, cheese, milk, and juice. Pretty tough to come up with creative menus!

Posted on: Fri, 03/16/2001 - 6:30am
SusanMO's picture
Joined: 03/13/2001 - 09:00

All I can say is food allergies are so confusing!!! Confliciting test results, conflicting doctor opinions, a whole array of varying reactions, etc. etc. My son too tested positive for skin and negative on the RAST. However, he has had a history of reactions. We did a food challenge (I started a thread on this) earlier this year because my doctor thought my son may have outgrown his allergy because of the negative RAST. WRONG!!!! advice to you, is don't believe the RAST to be the gospel truth just yet. Still avoid peanuts, carry that Epi and be safe!

Posted on: Fri, 06/14/2002 - 10:13am
5boysrus's picture
Joined: 06/06/2002 - 09:00

If any of these posters are still on this board I would like to know how things are for them now. My son had 5+ test for peanuts and negative (.05-whatever that means) for RAST. Don't know what to think. Never has had serious reaction but has been having more reactions to being around peanut and eating a cookie with it in (chest tightness, some intestinal symptoms over a day). ?? Emotional or allergic? not sure. probably goign to do food challenge sometime this summer.

Posted on: Sat, 06/15/2002 - 10:11am
BENSMOM's picture
Joined: 05/20/2000 - 09:00

Hi 5boysrus, I'm still around. I did take Ben to see Dr. Wood at Hopkins and had a CAP RAST done on him. It came back over 100--off the charts [img][/img]. Both the doctor and I were very surprised and his only explaination was that perhaps Ben had never been exposed to enough peanut to have a reaction. It wasn't the news I was hoping for. As for your son, I read some of your other posts and don't know what to tell you. It's hard to say if he's allergic or not, but the RAST result sounds promising.

Posted on: Sat, 06/15/2002 - 10:47am
anonymous's picture
Joined: 05/28/2009 - 16:42

Emily, My daughter's allergist told me last week that a 0.0 on a cap rast is ZERO. End of discussion. I am confused by some posts here that the blood test can have false negative results. That is exactly the opposite of what I was told.
I understand that the skin test for peanuts often has false positives and the cap rast for peanuts often will show a "sensitivity" but that person may not actually have an allergic reaction to peanuts.
Has anyone else been told that the cap rast test can have false negatives?


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