Posted by KaraS on September 5, 2004, at 15:36:59
In reply to Re: allergy testing » KaraS, posted by Larry Hoover on September 5, 2004, at 10:11:37
> > Honestly, I think there was only one thing missing: in one of Simus' posts about the kind of food sensitivity test she had done. You said that there were good tests for this and not so good ones. She mentioned RASP and either ELISA or ERISA (I think it was the former). The ELISA/ERISA one I believe is what I had years ago. That's the good one, isn't it?
>
> Food sensitivies/allergies are a huge conceptual quagmire. There is a lot of psuedoscience in there.
>
> RAST can be very useful. It is a test of IgE response to allergens. For that, it works beautifully, but.....
> a) it is most useful for inhallant allergens (e.g. pollens, spores)
> b) it has a strong negative predictive utility (i.e. no RAST response is a pretty good indication that the body is not sensitized (90% utility on negative responses))
> c) positive tests are merely suggestive. Only if a food history indicates a possible sensitivity, and the RAST is positive, should there be any clinical response (e.g. food elimination/rechallenge, or better yet double-blind food challenge (best done in the doctor's office, because if you have a serious response, it is an emergency)).
>
> ELISA is a test for IgG response. Everybody has IgG responses to food, and, in fact, IgG responses may be protective against IgE responses (which can be fatal). All formal allergy specialists (doctors with extra years of study in residency programs) dismiss ELISA as an unreliable measure, except when its results bolster the RAST, and food diaries.
>
> See: http://www.tldp.com/issue/174/IgG%20Food%20Allergy.html
>
> RAST itself is perhaps a "lazy man's" version of skin prick tests. But, even those can be unreliable, as most of the food extracts are not stable (they are perishable). Same goes for the RAST reagents. They are notoriously unstable. RAST *is* an excellent way to determine e.g. peanut, shellfish, wheat, etc. allergies, as most of the top allergens do have stable and reliable allergens to employ in the tests. It gets less reliable the more you move away from the most common allergens.
>
> Moreover, even a negative test (via RAST or skin-prick) does not guarantee the absence of allergy, or cross-reactivity. Peanut allergy can show up as an allergic response to licorice. An allergy to birch pollen can make you react to apple skins, but only when the offending pollen is sensitizing you (i.e. only in the spring). It's a very messy and illogical environment.
>
> The take-home message is that RAST (better) and ELISA (far less reliable) are starting points for investigations, not points from which conclusions can be reached.
>
> You may get a lot out of perusing this site:
> http://www.allergy-clinic.co.uk/food_allergy_testing.htm
>
> > P.S. How old are your two sons?
>
> Alexander is 12 (but his voice is changing, and he's already acting teenage, and he is almost as big as me). Thomas is 10, and even he is over five feet and 105 lbs. The food bills are already outrageous. Thank god I love to cook.
>
> Lar
Thanks. Bottom line it sounds like you can't completely rely on any food allergy tests unless it's for a few specified foods?Do either of your sons have your database mind?
-K
poster:KaraS
thread:384584
URL: http://www.dr-bob.org/babble/alter/20040901/msgs/386768.html