Are there any false positives with Rast, Cap-Rast or Skin testing?

My dd had positive skin testing for citrus and milk. She had the RAST for milk which later came up negative.
We kept my dd away from all milk proteins and citrus for about four months. After they were introduced again there were no reactions. The doctor told me that since her RAST to milk was negative that her skin test was probably a false positive and that since she was tolerating citrus without problems that that was also a false positive. He explained that the skin tests give "clues" of what to watch for.
I want to have DS tested for allergy, but my pediatrician advised me to wait since he is only 2 1/2. He told me that there was a much higher chance of having false positives at his age even on the RAST.
Maggie
[This message has been edited by maggie0303 (edited July 23, 2003).]

emom - I should mention that I want to have DS tested because of the strong likelihood for him to have allergies; family history (PA sister), eczema, etc. and I know he has reacted to cats/dogs. I do not plan on him having any nuts at all until he is tested.
I wonder if the doctors would think differently about testing him at his age if he had a pn reaction.
Also, related to your other thread on testing; our allergist said that he would not do another pn/tn skin test on dd due to exposure. He said we can recheck her Cap RAST every few years.
Maggie

Hi e-mom,
I raised a thread for you that may offer some info. In our situation, when my son was tested, we first used the Rast (6 years ago), he was 14 mo old. He tested positive (>100 level 5)peanuts, (level 3) for 2 tree nuts, (level 4) for milk and egg. Along with this info, our allergist used my son's reaction history to determine what he is allergic to. We have, since, used the Cap-Rast.
At that time, he also tested positive for wheat (level 2) and soy (level 2). We challenged, no reaction, and he has eaten these foods with no problem ever since. So, a positive result alone does not determine that somebody is allergic. But if the levels or numbers are above a certain point (different for each food), there is a much greater chance that they are really allergic.
Good luck,
Andrea
[This message has been edited by ACBaay (edited July 24, 2003).]

I agree with ACBaay.
Ryan first tested postive (>100) to peanuts at age 4. Two months ago, his second CAP RAST was 64 to peanuts, and also had him tested to some major tree nuts. The almonds came back at .99, and walnuts was 1.24, and cashews was 1.54 if I'm remembering correctly and borderline negative to pecans. Quite a bit lower than his CAP RAST for peanuts. He never had a reaction to tree nuts although we have avoided them since a PA diagnosis. The allergist said these are probably false positives, but to avoid for a while longer to examine subsequent CAP RASTS.

Here is my story: I have 2 children - 5yo dd and pa 2yo ds. My daughter has been diagnosed with asthma since 17 months old. the allergist apparently tested her for various things, including peanut. All were skin prick tests. The peanut test came up positive at 3+. The allergist never really followed up on it with me. As far as I can remember, he never even told me it was positive ( I found out YEARS later when we started seeing another allergist and my son was diagnosed with peanut allergy). Apparently the first allergist didn't think it was significant. Her total IgE was only 23 at the time.(not the peanut specific Ige, but the TOTAL Ige). They never did a RAST to confirm the peanut. THe second allergist didnt deam it necessary to do RAST testing either. Probably because she does not exhibit the clincial symptoms when she consumes peanut. Although we don;t allow peanut in our household, my daughter does eat it without problem at my mom's house. My feelings go 2 ways...either it was a false positive skin test....or she did indeed have the allergy and fortunately never had the anaphylaxis to go with it, and posssibly outgrew it??? She did have REALLY BAD eczema as a toddler and a good many asthma problems...(she was also eating peanut butter regularly.) I feel like she may have outgrown the allergy, since I too was once diagnosed with allergy to peanut (as a small child) , but can now consume it safely.
On the other hand, maybe her skin prick was a false positive. my allergist says 50% of skin prick can be false positive.
When I think back a few years ago to her results and if I would have only known what I now know today due to my ds Pa......it really scares me!