Are skin tests truly accurate??

Hi redtruck,

Our experience thus far on skin tests are this. PA son had no eczema at the time of skin tests and tests positive to peanut. Year later, tested for tree nuts and tests negative to those and positive again to peanut.

Now my eczema infested non pa daughter was tested to over 25 allergens and tested all negative. All of these skin tests however were done on the arm....I know some of your allergists do them on the back and I wonder sometimes if one area of the body is more sensitive?

I have just read skin tests are sometimes inaccurate due to a high ratio of kids being tested that have eczema and that may interfere with skin test results, which did not happen in our case.

Anyway, I look forward to reading this thread, good question redtruck!

Hi Redtruck,

It's good to see your name around the boards again.

In our experience with skin testing, my son kept testing positive to egg every year. Finally, he tested negative and has eaten eggs without any problems.

As far as peanuts go, his first introduction to them resulted in an anphylactic reation at 10 months of age. His face was so swollen, I did not recognize him! Not that we needed confirmation after that, [img]http://uumor.pair.com/nutalle2/peanutallergy/wink.gif[/img] the allergist did a RAST test to confirm his peanut allergy.

I do have a friend whose child tested postive to peanuts by skin testing (child had not eaten them though, they were testing her for the *common* food allergies because she had an anaphylactic reaction to milk.) She was recently re-tested for peanuts and the results were *negative.* (Trying to send hope your way). [img]http://uumor.pair.com/nutalle2/peanutallergy/wink.gif[/img]

Here is a link called *Allergy Testing* at [url="http://www.keepkidshealthy.com/welcome/commonproblems/allergy_testing.html"]www.keepkidshealthy.com/welcome/commonproblems/allergy_testing.html[/url] and the paragraph regarding *Prick Skin Test* is about half way down the page.

One thing we had to do before my son had his yearly skin testing was to make sure he did not have any antihistamine meds in his system prior to testing. This can give you false results as mentioned in the above link.

I wish you and your child well.

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Stay Safe.

[This message has been edited by Connie (edited July 06, 2002).]

The way I understand it, skin prick tests result in quite a bit of false positives, but very few false negatives.

In our case, skin testing has been accurate for both kids, except Matt tested negative to almonds and he's since reacted to trace almond residue twice. (I've never let him eat any, despite the negative test result)

Has your daughter ever had a CAP-RAST test for peanuts done? If I were in your shoes, that would be my next step. CAP-RAST testing (for peanuts, at least) is MUCH more accurate than skin testing. If she tests positive on the CAP-RAST I would assume she is definently allergic to peanuts, but if she tests negative, or under 20% of the 95% positive predictive value for peanut, I'd go one step further and try a food challenge...ONLY at the hospital, of course!

Keeping fingers crossed that NO history of reactions means NO allergy in your daughter's case!! =)

Thanks all for your responses...keep them coming!

No we haven't had a CAP RAST. I'll have to ask the dr. when we go later this month about that, and about any scores.

Her skin test was positive for peanuts, walnuts, and not conclusive on pecans. We'll see how it works out this time. Not really expecting any changes in results, but always hopeful.

Our allergist has said that skin tests have a 50% false positive rate. She only uses them in conjunction with a "real life" reaction. She hasn't skin tested our daughter for nuts or peanuts because she had obvious allergic reactions to them, and she (the allergist) felt there was no reason to do it. At this point I would never consent to it because I've read here about kids having severe allergic reactions to the testing. I also feel that it could count as an exposure. We did have the Cap Rast done in December and unfortunately our daughter tested very high for both peanuts and walnuts.

50% false positives?! wow, that pretty high! Interesting. How accurate are these rast tests?

My allergist says the same thing about the skin pricks being 50%....My 1 yr old son tested 3+ on the skin prick for peanuts. We had him tested for peanuts after an exposure which sent him to the ER with severe reaction. Oddly enough, my 4 year old non peanut allergic daughter went to the allergist just last week to be tested for seasonal allergies-ie pollen, etc. Our new allergist reviewed old notes from the prior allergist and just informed me that my daughter also tested 3+ for peanuts at age 17 months. The allergist told me to allow my daughter to continue eating the peanuts and that the skin prick test was false positive....It really makes me wonder....hopefully if you have the RAST it will clear up whether or not the allergy is really there....

Hi redtruck. I remember that we're in the same boat. My son is the same age as your daughter, had a mild reaction (one bump on mouth) to walnuts, which if I remember correctly is what your daughter reacted to, and has never reacted to peanut residue or cross contamination or peanut flour in granola bars he ate every day for 6 months. He was a 4++ on a skin prick test as well as positive for all other nuts except, you got it, pecans.

Are skin prick tests accurate? Hardly. As someone else said, they're good for ruling things out--false negatives are rare, but false positives? 50% is generous. Dr. Wood (leading pa doc out of Johns Hopkins) told me that only about 30% of people who react positively to a skin prick test will actually react to the allergen. So, they're mostly a ruling out test, not a diagnostic test.

Ben did have a CAP RAST since I was doubtful about the whole allergy thing. Well, he was over 100 for peanut which is off the chart and means he should be expected to react to minute amounts and would be expected to react about 100% of the time that he's exposed. That hasn't happened so it doesn't make sense to me. His walnut score, the only thing he's ever reacted to was low, and the other tree nuts were low, although pecan, if you can believe it, was higher. Dr. Wood thinks he may be outgrowing the tree nut allergy. SO, I would be very interested in your daughter's CAP RAST results and I'm totally fed up with allergy testing and how non-informative it can be--rant, rant! Despite my annoyance with testing, I would get your daughter the CAP RAST and see what it says.

Hi Bensmom, yes i remember now how similar our situations are. I dont have any scores for previous skin tests. At our appointment, i'll definately be asking about this cap rast, and more about the skin test reliability. I'm learning new things everyday! I do remember the allergist saying that 10 years ago, he wouldnt even have recommended an epipen for her (based on the results of the skin tests he performed!).

Now i'm starting to wonder if we should subject my daughter to another skin test?!
We definately want to have my son tested for the first time, but wonder how we should handle retesting my daughter...am i just exposing her for nothing?

Here`s what our allergist who is affiliated with UCLA School of Medicine says. He says that the size of a positive skin test does not correlate with the severity of the allergy. You can have a large skin test with a mild allergy to something or vice versa. He also quotes a 50 % false positive but says that is usually after an allergy is outgrown, the person can have a positive skin test and no longer be allergic. He quotes a false negative of 3%. That was us---my daughter was skin tested for egg at age two and a half. She was negative so three days later I gave egg and had to use the Epipen. I was so shocked that it looked like anaphylaxis, yet I had just been told she wasn`t allergic to egg, that I`m glad I was able to pull myself out of my shock and get it together to use the Epipen. A few weeks after that she was skin tested again for egg and was postive which she still is. She is skin test positive for peanut with a high CAP-RAST. Since I never gave her peanut due to her milk and egg allergy, her high CAP-RAST and positive skin test had never been put to the test until I gave her a product made on shared equipment with peanuts and not stated, and she had a reaction. So the CAP-RAST is pretty accurate.

Well, thursday (tomorrow) is the big day for us. We visit the allergist for the test on my 3 yr old, and then have to decide if we retest my 6 yr old. I guess we'll decide tomorrow based on his recommendation, and if my daughter gives us a hard time about it. I'll let you know what happens, especially if theres any change. Here's to hoping my son isn't allergic at least.

I know my dd was eating sesame contaminated and containing foods and never reacted. When we saw the allergist first time, skin scratch was + for sesame. I asked on follow up, about her having eaten them and seemed fine. He said in the instance of known ingestion with no reaction, a + skin scratch does not neccessarily indicate allergy. He did a rast, and it was negative. She was + at that first visit to skin scratvh on some tree nuts, and the rast was negative for tree nuts(all of them) this follow up.

Of course, I do not plan to feed her any nuts and it seems easier to avoid sesame as a general rule of thumb in obvious situations. I want to keep consistent since at 2, she has he allergies memorized, and I do not want to confuse her! I do feel less anxious though about crackers and cross contaminations with this new info.

Just anecdotal, but thought I would share. She had mild eczema as a baby, skin is pretty good since about 9 months old. becca

[This message has been edited by becca (edited July 24, 2002).]

thanks becca for your input. my daughter too had eczema. i wonder if that contributes to + skin tests since their skin is a little more sensitive?
In reading other topics here related to outgrowing etc., i think if we ever had the good news about her not being pa, we would still avoid nuts, but let her have the may contains etc. at least for a few years!

We went for our skin test on thurs and luckily at least my 3 yr old son is NOT allergic according to the test...yippee!
My daughter showed no signs of tree nut allergy this time (previously she test + for walnuts and poss. pecans). She still showed + for peanuts, but it was smaller now he said, and overall, its generally not large to begin with (I dont know scores, but i did see the nurse write down 3x3 after she measured it in mm).

She is going to get a cap rast to confirm results for peanut, and a few tree nuts.
I asked him how accurate the skin test is, and he seemed pretty convinced on its accuracy.

Anyway, at least there was some good news that day!

Congratulations on the news that your son is not PA!

We have had a somewhat similiar experience with skin testing with Adam's younger brother.

He was skin tested at age 2 years 3 months, at the time we were investigating other allergies (not food). He came up positive to peanut, despite no known exposures.

We were told to have him tested yearly, primarily due to the incidence of false positives. Once he had 2 negative tests, he could be orally challenged. Cap rast testing was never suggested.

Two years later with 2 negative skin tests, he was challenged at Sick Kids. Luckily, he is not PA.

my 2 cents worth- DD had tomato and peanut butter when she was 13 months old ( 2 new foods in the same night, what was I thinking?). had a reaction of some facial swelling and body rash (warm to the touch). RAST tested a Level 3 to Peanuts after that. Assumed she was allergic to PN and have avoided ever since. At 3 yrs old, had CAP-RAST tests done. ALL HER CAP-RAST TESTS TO PEANUT, NUTS AND SHELLFISH WERE NEGATIVE!!!! We then skin tested her and she came back positive to peanut and cashew (and tomato--by the way)...So, is she still allergic to PN? Who knows...Doctor said to keep her away and we will re-test at 5. I know I have read things that you can continue to test postiive on the skin after outgrowing an allergy. BTW, she eats pasta sauce, ketchup and salsa with NO problem...Is the skin test for tomato wrong???

The more responses to this topic, the more confused i become. Are kids without reactions just testing positive to skin tests or are they truly allergic? Everyone seems to have a different answer, from my allergist, to all the opinions on this board.
This is very disturbing!
Perhaps i'm just oversimpifying, cause most people probably have a reaction before they test, so that just leaves me more confused.