RAST testing - Peanut Allergy Information

RAST testing

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HI ! We self diagnosed our daughter, Hannah ,as having peanut/tree nut allergies. We recently decided to have her tested using the RAST method. To our confusion and surprise , the test came out negative in regards to nuts.

Hannah has anaphylactic reactions after eating nuts. Has been hospitalized once. Even the doctor was perplexed why the results said "no allergy to nuts". Just two weeks ago , she broke out in hives after accidentally eating something with nuts in it.

What do I do now ? She's only 5 years old so I really hate to put her through more tests. Thanks for any help you can give. Jennifer

On Nov 25, 2002

What else was in the products she ate? Maybe, she has another allergy.

Lab testing is not 100% accurate. If she is having reactions to nuts, then please don't let her eat them.

On Nov 25, 2002

I`d have it repeated, but have them do a CAP-RAST. I don`t think a RAST is all that reliable, but a CAP-RAST is. I know it is another needle stick, but it seems like it would be worth it. Sounds like maybe the lab made a mistake. I agree with the other person that said don`t give her nuts or peanuts, even if it is negative.

[This message has been edited by Carefulmom (edited November 25, 2002).]

On Nov 30, 2002

what is the difference from a Rast test and a Cap Rast test? My son had a blood test, but I don't know if it was a Cap Rast or a Rast? He was a 4+ on peanuts. very bad. thankyou

On Nov 30, 2002

I'm not 100% certain about this (I'm not a doctor, and don't even play one on tv [img]http://uumor.pair.com/nutalle2/peanutallergy/smile.gif[/img] ), but it was my understanding that the CAP-RAST was simply a newer and improved version of the RAST test, and that any blood test that's been done in the past couple of years was in fact a CAP-RAST, not a RAST, which I thought wasn't available any more (although, of course, I could be wrong).

When my son had his first reaction to peanuts, we had his allergy testing done by his pediatrician, since we didn't yet have an allergist for him. The pediatrician only did blood tests, not skin tests. What the pediatrician told us (and seems to jibe with what other people have posted here) is that blood testing can give false negatives. It is extremely unlikely to give false positives, however, so if the blood test (i.e., RAST or CAP-RAST) tells you you're allergic to something, you almost certainly are truly allergic to it. If it says you're not allergic, you may or may not truly be allergic to the allergen in question. This could be what happened to Jennifer1970's daughter.

Skin testing, however, more commonly gives false positives, and only rarely gives false negatives. (I should mention, though, that I personally have had a false negative skin test. My reactions to bananas are clear enough that I *know* I'm allergic to them, even if the skin test tells me they're fine for me.) Another downside to skin testing is that each skin test is an exposure to the allergen you're testing for, and if you believe that each exposure to the allergen makes your child less likely to outgrow the allergy and worsens the severity of future reactions, then skin testing is a bit of a concern. Whether Jennifer1970 wants to expose her daughter to peanut protein in order to have a skin test is a personal choice, and a tough one at that.

Personally, if it were me, I'd pass on the skin test for now, given that Hannah has had anaphylactic reactions, and live as if my child were clearly allergic to peanuts and treenuts. Then in a year or two, I'd repeat the CAP-RAST to see if anything had changed. I don't know if the skin test would be worth risking until a good number of years had passed without any reactions and with continued negative blood tests.

FWIW, Debbie