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

Posted on: Wed, 07/23/2003 - 1:05am
e-mom's picture
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Please tell me your stories about any false positives with Rast, Cap-Rast or Skin testing.

Posted on: Wed, 07/23/2003 - 1:28am
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Joined: 04/14/2003 - 09:00

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).]

Posted on: Wed, 07/23/2003 - 8:29am
e-mom's picture
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Thanks maggie0303. That really interesting about the chance of having a false positive at that early age.
Hmmmmm. What to do? What to do?

Posted on: Wed, 07/23/2003 - 1:23pm
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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

Posted on: Wed, 07/23/2003 - 9:26pm
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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).]

Posted on: Thu, 07/24/2003 - 12:24am
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Joined: 05/28/2009 - 16:42

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.

Posted on: Thu, 07/24/2003 - 12:30am
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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!

Posted on: Thu, 07/24/2003 - 7:30am
e-mom's picture
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Thanks Maggie,
I am definitely not going to have PA ds skin tested--I just don't want to take the risk. I'm definitely thinking Cap Rast.

Posted on: Thu, 07/24/2003 - 7:44am
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ACBaay,
WOW, thanks for raising that old thread. I printed it out and plan to keep it in my pa files.
This is going to help me considerably when I go speak with the allergist.
These tests remind me a lot of the QUAD tests when I was pregnant. Having the tests reading a negative doesn't necessarily mean that the baby won't have something abnormally wrong with him. AND having the tests reading positive doesn't necessarily mean that there is something wrong. TONS of high false positives!!!!! In fact, the QUAD tests leaflet states that all 4 of these tests have false positives. UGH!!! Sorry this is a whole other story for me.
What's the point in getting these tests done if there are going to be false positives?

Posted on: Thu, 07/24/2003 - 7:49am
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Quote:Originally posted by ryan's mom:
[b]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.[/b]
The only test that I had done for PA ds was the skin test (at the time it was what was recommended by his allergist).
She has tested him for 8 other nuts and included sesame.
Fortunately, he tested negative to all of the other nuts and sesame. No redness or welts at all.
He only tested positive to peanuts. His welt was the size of a quarter.
However, it was recommended that we keep him away from all nuts due to cross contamination.
I wish this were easier. I just want an accurate test.

Posted on: Thu, 07/24/2003 - 8:01am
e-mom's picture
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Quote:Originally posted by austin2001:
[b]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![/b]
Yes, it is a scary story. Thank you for sharing it. It's stories like these that are really opening my eyes about these tests. So frustrating.
So you daughter first tested positive to having a peanut allergy, allergist never told you it was positive, she continued to eat peanut butter and has ever since without ANY type of reaction?
Wow, either you are really lucky (or I should say the allergist is really lucky--lawsuit) that she never had a reaction or she, in fact, did have a false positive.
Did she ever have any type of reaction from eating pb that you know of?

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