Anyone have a known incorrect RAST tests for any food?

Posted on: Mon, 03/06/2006 - 5:55am
Danielle's picture
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Joined: 04/08/2003 - 09:00

I know that RAST tests can be incorrect but I am wondering how many have actually had an incorrect test. At this time, I am wondering about other foods other than peanut. My mfa daughter had a neg RAST just come back and now we are scheduled for a skin test. She had 2 terrible hives reactions about 5 weeks ago within 12 hours of each other. Both required me to take her to the hospital and then 10 days of steroids, beni, zyrtec... blah blah. It was bad but no epi was needed. All the things that it could have been came back negative. She has in the past had some wrong RAST results.. I am still betting on that is was dairy. Anyway, I am just wondering....

[This message has been edited by Danielle (edited March 06, 2006).]

Posted on: Mon, 03/06/2006 - 6:03am
Daisy's picture
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Joined: 01/16/2006 - 09:00

I am an adult with food allergies. Used to be all GI, now they have resp symptoms, also. Never had hives with foods.
Yes, some of my RAST have been negative, sometimes they are positive. My allergist explained that sometimes with extreme avoidance, your "memory response" may drop, especially in GI allergies. But skin testing has always been positive.
Daisy

Posted on: Mon, 03/06/2006 - 6:44am
mommyofmatt's picture
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Joined: 03/12/2004 - 09:00

Yes, our last RAST to dairy was negative, skin test was positive. DS failed the milk challenge -- he got a giant hive after drinking 1 part milk to 100 parts water.
Allergist declared him still allergic and to practice strict avoidance for another year. Meg

Posted on: Mon, 03/06/2006 - 7:03am
Daisy's picture
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Joined: 01/16/2006 - 09:00

see if this helps...
11/19/04 re: Peanut sensitivity
The patient is a male, age 2 +. The symptom he presented with was hives. According to the mother, there is peanut allergy in the family history. He was treated with 3 courses of prednisone and each time the patient improved, but the hives returned. ImmunoCAP testing was performed on 8/17/04. The results were completely negative with a total IgE of 21KU/L. The child still had symptoms, hives, and was referred to an allergist. The allergist did scratch testing on 8/23/04. That testing showed that the child was allergist to peanut, molds and English Plantain. Since the peanut has been removed from the child's diet, he has had no more hives. How can these tests come up with completely different results? Is this a non-IgE mediated reaction to peanuts?
To help respond to your question, I obtained input from Dr. Scott Sicherer of the Mt. Sinai Medical Center in New York City. Dr. Sicherer and his colleague Dr. Hugh Sampson are leading experts in the investigation of food allergies, particularly allergy to peanuts. His comments are enclosed below. When Dr. Sicherer mentioned his impression that your patient was clinically reactive to peanut ingestion, I think that he based this on the fact that the urticaria cleared when peanuts were with held without other changes in the diet or medications. However, as he and Dr. Sampson have shown clearly, a cautious oral challenge with the suspect food is the "gold standard" in such matters, assuming that such challenges do not present risks for a severe reaction (e.g.- anaphylaxis). As pointed out by Dr. Sicherer below, in cases proven by a positive oral challenge, the skin test can be positive in face of a negative CAP RAST.
Dr. Sicherer's comments:
If I understand the question, this child had immediate allergic reactions to peanut and had a negative serum test for peanut-specific IgE antibody but a positive test to peanut by skin test. This is no surprise at all. The skin test is more sensitive than a serum test. This is why a history is the most important part of the evaluation. When a history is convincing, the a priori reasoning changes to "expect" a positive test if the correct cause is identified. If the result is surprising (blood test negative) one would go to a more sensitive test such as the prick skin test before doing a food challenge to confirm the situation. A negative serum test to peanut, but a positive prick test, with an actual clinical reaction, occurs about 15% of the time
[url="http://www.aaaai.org/aadmc/ate/foodallergy.html"]http://www.aaaai.org/aadmc/ate/foodallergy.html[/url]

Posted on: Mon, 03/06/2006 - 6:03am
Daisy's picture
Offline
Joined: 01/16/2006 - 09:00

I am an adult with food allergies. Used to be all GI, now they have resp symptoms, also. Never had hives with foods.
Yes, some of my RAST have been negative, sometimes they are positive. My allergist explained that sometimes with extreme avoidance, your "memory response" may drop, especially in GI allergies. But skin testing has always been positive.
Daisy

Posted on: Mon, 03/06/2006 - 6:44am
mommyofmatt's picture
Offline
Joined: 03/12/2004 - 09:00

Yes, our last RAST to dairy was negative, skin test was positive. DS failed the milk challenge -- he got a giant hive after drinking 1 part milk to 100 parts water.
Allergist declared him still allergic and to practice strict avoidance for another year. Meg

Posted on: Mon, 03/06/2006 - 7:03am
Daisy's picture
Offline
Joined: 01/16/2006 - 09:00

see if this helps...
11/19/04 re: Peanut sensitivity
The patient is a male, age 2 +. The symptom he presented with was hives. According to the mother, there is peanut allergy in the family history. He was treated with 3 courses of prednisone and each time the patient improved, but the hives returned. ImmunoCAP testing was performed on 8/17/04. The results were completely negative with a total IgE of 21KU/L. The child still had symptoms, hives, and was referred to an allergist. The allergist did scratch testing on 8/23/04. That testing showed that the child was allergist to peanut, molds and English Plantain. Since the peanut has been removed from the child's diet, he has had no more hives. How can these tests come up with completely different results? Is this a non-IgE mediated reaction to peanuts?
To help respond to your question, I obtained input from Dr. Scott Sicherer of the Mt. Sinai Medical Center in New York City. Dr. Sicherer and his colleague Dr. Hugh Sampson are leading experts in the investigation of food allergies, particularly allergy to peanuts. His comments are enclosed below. When Dr. Sicherer mentioned his impression that your patient was clinically reactive to peanut ingestion, I think that he based this on the fact that the urticaria cleared when peanuts were with held without other changes in the diet or medications. However, as he and Dr. Sampson have shown clearly, a cautious oral challenge with the suspect food is the "gold standard" in such matters, assuming that such challenges do not present risks for a severe reaction (e.g.- anaphylaxis). As pointed out by Dr. Sicherer below, in cases proven by a positive oral challenge, the skin test can be positive in face of a negative CAP RAST.
Dr. Sicherer's comments:
If I understand the question, this child had immediate allergic reactions to peanut and had a negative serum test for peanut-specific IgE antibody but a positive test to peanut by skin test. This is no surprise at all. The skin test is more sensitive than a serum test. This is why a history is the most important part of the evaluation. When a history is convincing, the a priori reasoning changes to "expect" a positive test if the correct cause is identified. If the result is surprising (blood test negative) one would go to a more sensitive test such as the prick skin test before doing a food challenge to confirm the situation. A negative serum test to peanut, but a positive prick test, with an actual clinical reaction, occurs about 15% of the time
[url="http://www.aaaai.org/aadmc/ate/foodallergy.html"]http://www.aaaai.org/aadmc/ate/foodallergy.html[/url]

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