conflicting RAST/skin results


hi all, i'm totally confused about my daughter's test results. about two months ago we had her skin tested for egg and peanuts and she tested positive for both. two big bumps appeared pretty quickly. so we took her back (along with her twin brother) to have more tests done. the doctor ordered a blood draw for RAST tests for each. i got my son's back showing he has a level 2 egg allergy and nothing else (no big surprise). i just got my daughter's RAST results back and it only showed a level 1 egg allergy - no peanuts!!!!!!!!!!! what does this mean? how am i to interpret this? have any of you experienced this? which test is more accurate? our allergist is out of town until tuesday so i have to wait until then to get more info. thanks!

On Jun 10, 2005

When we went for testing with my son, we were told that you can get a false positive with skin prick testing, and that if his skin prick turned up positive (it did), that we would need to follow with a RAST test to confirm the allergy (and in our case it did).

I hope this means your daughter is in the clear!

[This message has been edited by happycat (edited June 10, 2005).]

On Jun 10, 2005

If the CAP RAST score is less than 0.35, it may register as "negative". My allergist sent my daughter's bloodwork to a second lab (Mayo) which tests for levels under 0.35. Walnut was negative per the 1st lab, then Mayo showed it at 0.12.

On Jun 10, 2005

My son is 2 1/2 and had a SPT at 18 mos. and showed positive quickly to Peanut and negative to everything else. Then, at 2 he had the CapRAST done and it was negative to Peanut, but positive to Egg. We have been avoiding Peanut ever since the SPT and now also avoid egg (only in the raw form, he is able to tolerate it cooked)since the reason we had his RAST test done was becasue we were noticing he was allergic to something and we couldn't link it to peanut. So, long story short, our allergist said that since my son is still so young and his immune system is still developing, a positive SPT is a pretty good indicator that an allergy is present, however along with the negative RAST he has a decent shot at outgrowing it. Of course that is not a guarantee. Our allergist would like to do a RAST test once a year until my son is 5, at which time he said the immune system stabilizes and if my son is still showing negative to the RAST he would do a SPT and if both are negative, then a Peanut Challenge. So, while we hate the wait, we would rather err on the side of caution while he is still young, especially if he has a better chance of outgrowing the allergy by avoiding peanut. Sorry for the long response, but we had the exact same thing happen to us and we were also totally confused....hope this helps.

On Jun 11, 2005

I had a similiar result. My son was skin tested for typical food allergies, but tested for peanuts/tree nuts. showed allergy to soy, egg whites and strawberries. Then, when he was almost 4, he had ana. reaction to peanuts. a skin test showed a 16mm wheal.

this year, son is 7 we did rast for egg whites, shellfish and peanuts. The egg and shellfish were negative and the peanut was 1.3 or so which indicated that he may have outgrown the peanut allergy.

so, a skin test was done to confirm rast. the egg and shellfish were again negative, but the peanut produced a very large wheal. So, the dr said that we need to continue to avoid peanuts and we'll do rast again in 6 mo to 1 year.

i can't remember all the reasons for the conflict in results. I was so disapointed that he didn't outgrow the allergy.

On Jun 11, 2005

Here's my take on the two results, FWIW. My understanding is that a negative skin test is about as accurate as it gets in determining the absence of an allergy. But skin tests can produce false positives.

RAST TESTS can produce false negatives. My ds failed a milk challenge after he tested negative on the RAST and had a positive skin test.

So you have to look at reaction history (if any) the results of both types of testing, and the child's age to determine if you want to do a challenge in a doctor's setting.

My ds without allergies has only had skin testing done, they were all negative. We will let him eat milk products when his brother's not around, but we still clear of nuts with him too since they're just 3.

Sooooo frustrating with how these tests are not exact. Good luck.

------------------ ***[b] ALLERGY ELIMINATOR*** [/b]

Meg, mom to: Matt 3 yrs. PA,MA,EA Sean 3 yrs. NKA

On Jun 11, 2005

DS had a postive SPT to soy at his 12 mth check up.....then did a RAST and it came back neg. So we repeated SPT for soy at 18 mths and it was neg (a true neg since he has eaten bread with soy flour since)

They said that either the needle they used to do the egg (one of his allergies) skin prick wasn't wiped off all the way before they did the soy one OR a bit of the egg spt liquid dripped over into the soy area

so maybe something like this happened to you as well

On Jun 13, 2005

DS has skin tested postive to sesame and watermelon but RAST tested negative for both. It is very aggrivating to me because I'm trying to write his 504 plan for September and I don't know what allergies to list.

On Jun 14, 2005

My son had a positive skin test and a negative RAST test. His allergist advises waiting until he is 4, doing both tests again and them possibly proceding with a food challenge.