CAP RAST results question

Posted on: Thu, 07/01/2004 - 12:02pm
mistey's picture
Joined: 01/18/2004 - 09:00

I'm sure the answer to this exists somewhere, but I had no idea what to even search under, so please bear with me . My ds's CAP RAST test results came back today and we were so pleased that he tested negative to bee venom, sesame seeds, lobster, crab, salmon, etc. But he has never been exposed to any of these things. If he has not been exposed, would these test results be valid? Thanks for any input!!

Posted on: Fri, 07/02/2004 - 6:27am
anonymous's picture
Joined: 05/28/2009 - 16:42

My youngest child was tested for peanut, tree nuts, lots of fish, and some other foods this past May. He is 5 and never had any of those foods before, with the exception of Mahi Mahi fish about four or five months ago. The only way he could have been exposed to any of these would be from breastmilk.
The skin test was done for all of the above. The RAST was done (second year in a row) for only peanut. Again it was negative. He did the oral challenge in the office since both skin and RAST were negative. He passed with flying colors.
My gut feeling, however, was that he would be negative to everything based on his health (lack of severe eczema) as a baby.

Posted on: Sat, 07/03/2004 - 12:48am
Carefulmom's picture
Joined: 01/03/2002 - 09:00

I posted the same question a couple of weeks ago when my daughter had Cap Rast done. I am anxiously awaiting to see if anyone knows the answer.

Posted on: Sat, 07/03/2004 - 2:13am
Lovey's picture
Joined: 03/22/2004 - 09:00

CAP-RAST tests can produce false positive or negative results but appear to be more accurate than skin tests.
Here is a link with a considerable amount of information including a little on the CAP-RAST and the possiblity of inaccurate results.
As with all types of allergies a person can develop them over time with repeated exposure to the allergens.
If a person already suffers from severe allergies, it's important to be aware of the potential for new allergies developing. This is not to live in fear but to live with awareness and care.
This is a quote from the link above in case it no longer works in the near future:
"RAST (radioallergosorbent test) is an in vitro measurement of serum food specific IgE. The test is more available and practical for primary care physicians to evaluate food specific IgE antibodies. It should be noted that RAST tests are heterogenous yielding potentially unreliable results. CAP-RAST (the Pharmacia CAP system FEIA) is a newer generation of RAST which provides more reliable quantitative measurements of specific IgE levels. Table 1 is a recommended interpretation of food allergen-specific IgE levels (kUA/L) by CAP-RAST in the diagnosis of food allergies (5). For example, if a child's egg-specific IgE level is 7 or greater by CAP-RAST, there is greater than 95% likelihood that the child is truly allergic to eggs. In contrast if the egg-specific IgE is less than 0.35 and there is no compelling history of egg allergy, there is a 95% chance that the child is not allergic to eggs. However, there is a 5% chance (1 in 20), that the child's CAP-RAST is falsely negative and that the child is allergic to eggs (as in case 4). If there is a strongly suggestive history of a food allergy, it should be noted that a low CAP-RAST can be misleading."

Posted on: Mon, 07/05/2004 - 11:33pm
jtolpin's picture
Joined: 05/28/2003 - 09:00

Quote:Originally posted by mistey:
But he has never been exposed to any of these things. If he has not been exposed, would these test results be valid? Thanks for any input!! [/B]
I used to say, it doesnt matter if hes exposed or not, they could still test + (and not have it be a false positive, but a TRUE allergy)
Case in point is Caitlin: (and my story has changed slightly, but still...)
Caitlin tested positive for the whole nut panel (peanuts, cashews, walnuts, pistachios, etc..)
DW is anaph to peanuts and (I thought) avoided all nuts... except for an occasional walnut on an apple pie...
I used to think allergies are just genetic... and Caitlin would be allergic to all nuts, regardless... we never rast'ed her for nuts until 3 1/2, no reason to... given her history of FA's, and DW's, theres no nuts in the house, kwim?
FF to present... Turns out, while PG with Caitlin, DW had pistacchio pudding. So, maybe C's pistachio allergy is due to that (she was >100 for them, and cashews, but just 'high' in all the others)
So, I STILL believe shes never had almonds, peanuts, cashews, either in utero, while BF, or through oral ingestion... Yet she tests positive to all of them... and I'm sure thye arent faslse positives, nor are we going to find out 'HOW ALLERGIC' she is to them. We'll just avoid all nuts going forward... And DW has given up the pistacchio pudding... Why she was eating it.... I just dont understand [img][/img]
Caitlin 4-17-00 Allergic to Dairy, Egg, Wheat, Bananas, Grapes, Rye, Sesame, Beef, Garlic, Mustard, Onion, Peas and Avoiding Latex and all Nuts
Sara 2-13-98 NKA (avoiding nuts)
Meghan 2-28-03 Outgrown Reflux - Alimentum feeder, Stopped Zantac - RAST neg to big 8

Posted on: Tue, 07/06/2004 - 2:57am
Westporter's picture
Joined: 06/25/2003 - 09:00

We just saw Dr. Michael Young (author of the Peanut Allergy Answer Guide) for a second opinion on my 2 y/o DS CAP RAST tests. He told us to get a CAP RAST test yearly to see if the numbers go down. My DS CAP RAST to peanut is low, (0.45). Dr. Young said that if the numbers go down and/or stay the same, he would definitely suggest a food challenge at age 7 for peanut, but not before then.
We got a second opinion from him only because my DS skin test was positive to peanut. Dr. Young said no test is perfect, but from here on in, do the CAP RAST annually not the skin test.

Posted on: Tue, 07/06/2004 - 3:44am
Lovey's picture
Joined: 03/22/2004 - 09:00

This link leads to the web site of Labspec, a diagnostic laboratory. There is a tremendous amount of allergy information there, including types of allergens, clinical experience, crossreactivity and diagnostic testing. It may help answer some of your questions and confirm some of your experiences.

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