Rast tests - don\'t match up with skin test..now what?

Posted on: Thu, 03/25/2004 - 12:13pm
ks65's picture
Joined: 03/06/2002 - 09:00

My ds had a anaphylatic reaction to something about 3 weeks ago. We already have kept him away from wheat, egg, milk and peanut...due to prior allergy testing. We did a CAP RAST blood test for many things. Well, a bit of history. At 9 months we did skin tests, he was 4+ to wheat and 4+ to egg (did not test milk b/c of a reaction and did not test peanut)..At 18 months we skin tested again, he was 4+ to wheat and 1+ to egg. The doctor said that he had outgrow the egg most likely and to try at home. We never did as I was too scared. So, last week at 2 1/2 years old he was CAP RAST blood tested....Egg - Class 4, Milk Class 4, Peanut Class 3 and Wheat--off the charts at Class 6. NOW, first of all...how can the egg be a skin test of 1+ (1 year ago) and now a Class 4 when he doesn't even eat it. It doesn't make sense. He eats wheat starch (Cheerios and Kix) and has for awhile...The Class 6 really boggles my mind. The peanut....well, to my knowledge he has never had it - not thru pregnancy or bfeeding...but I gather you have to be exposed to it to test positive. The doctor wants to food challenge him in her office in June to the egg (I think given the skin was negative)...Next, we would try wheat. We are NOT going to do the milk or peanut. BUT, I guess my question is...after all of this testing, I feel like I don't know much. Has anyone (or your child) had blood tests that say you are positive and you know you are not? For example, I have heard that some have a positive blood RAST to something (egg, wheat, etc.) and they have been eating it all the time and are in fact, NOT allergic. The doctor also mentioned that my ds could have grass/pollen allergies and therefore, the wheat is showing up as allergic and may not be. Anyhow, any thoughts are appreciated...I am just frustrated and sad. thanks

Posted on: Fri, 03/26/2004 - 12:39am
ks65's picture
Joined: 03/06/2002 - 09:00

just re-raising..i really would love to hear input/advice. thanks

Posted on: Fri, 03/26/2004 - 1:47am
becca's picture
Joined: 05/22/2001 - 09:00

My dd has had the opposite. She has some + skin tests(to sesame, various tree nuts) but neg. bloodwork. I brought up the sesame with my Dr., after avoiding it for a year, and he said with positive testing and no known reaction upon consumption, they assume there is no allergy. So, we no longer avoid traces of sesame, but try to avoid the obvious, because it is disconcerting to have a + test out there, I know.
The nuts we avoid anyway with PA, so I would never give her anything with trace nuts, etc...
So, I do not know if this helps, since it is opposite. Last time dd was tested for egg(we do not test the nuts anymore at present), the allergist dod skin only, saying it is more sensetive and reliable. Not sure why. But I also thought the skin test could be reactive even in the absence of allergy or with outgrown allergy. So, I too get confused. My dd has low test numbers, which dropped dramatically in a year, so I think about these things alot, hoping she is outgrowing and we might be able to challenge safely.

Posted on: Fri, 03/26/2004 - 4:24am
Scooby's picture
Joined: 04/09/2000 - 09:00

My DS has had several negative skin tests with postive CAP RAST for egg. We know he is allergic to eggs because he reacted on contact with egg-containing products. He has never ingested them. It is utterly frustrating!

Posted on: Fri, 03/26/2004 - 5:44am
mommyofmatt's picture
Joined: 03/12/2004 - 09:00

Ok, here goes. My ds tested mildly positve on rast and skin at 12 mos. to soy, wheat milk, and egg. Dr. said to try tiny bit. He's ok eating soy and wheat. He reacted to egg, and milk so we stayed away from it. He tested very high to peanut, obviously haven't touched the stuff.
We just redid his rast testing, came back w/egg higher (hasn't eaten any to my knowledge). Milk was lower, allergist, said he can most likely tolerate, let's play it safe and do a food challenge next week.
Then...he accidentally drank a tiny, tiny bit of milk today at playgroup, and reacted w/hives and itchy ears. Very bummed. I know this probably hasn't helped at all KS65, but that's our confusing deal.
Meg, mom to:
Matt 2 yrs. PA,MA,EA
Sean 2 yrs. NKA

Posted on: Fri, 03/26/2004 - 9:56am
cathlina's picture
Joined: 06/29/2001 - 09:00

My allergist tells me that skin tests are more sensitive than the blood tests.

Posted on: Mon, 03/29/2004 - 4:02am
austin2001's picture
Joined: 05/03/2002 - 09:00

I heard that skin testing is a 50/50 deal. IF you have any type of skin conditions like eczema, your results would be better determined by blood work, because the skin test may show false results. I have heard that skin tests can show 50% false positive.
On another note, I have a peanut skin test a t 4+ and a RAST of over 4.65?ish....I can eat peanuts without problem. My almost 3 year old PA son's RAST is lower than mine. His RAST was around 8 or 9 when he had his one and only (knock on wood) anaphylactic reaction to peanut butter at 9 months old. ....Yet again, I have a 5 yo dd who tested positive to peanut by skin test (3+) at 17 months old, but we were never advised to remove peanut from her diet. (she did during that period in her life have major eczema problems and asthma related illnesses.) Ironically, my PA son's initial skin prick at 9 months old was 3+ also.
It is very confusing. Hopefully in the near future there will be a test that can be done to determine if you are truly allergic to peanuts or not. I have recently read about this.
Well, that was my input - confused as much as me? [img]http://uumor.pair.com/nutalle2/peanutallergy/smile.gif[/img]
take care and stay safe!

Posted on: Mon, 03/29/2004 - 12:02pm
ks65's picture
Joined: 03/06/2002 - 09:00

Allison - thank you for your post. I am just so, well, in a funk...I guess so upset with the conflicting tests and well, just the high levels of the tests. I really appreciate the fact that atleast you tell me that from the "tests" you would be allergic to peanut, but are not. I am hoping that something like this applies to my son's wheat or egg allergy. I know he is allergic to milk and with the peanut..I am not even going to go there until he is older. With my daughter it is just so weird b/c she has not had a reaction since 13 months..and her blood test has been all over the board ( Class 3, Class 0 and now Class 4)....Anyhow, you give me some hope re: my son. I did talk to the lab today and they did do the Pharmacia Immunocap test which is the CAP RAST and the most sensitive reliable test out there as far as blood tests...I just keep thinking then that the blood tests must (or have to be) right...and then get depressed again!!! Who knows.

Posted on: Mon, 03/29/2004 - 12:32pm
megans mommy's picture
Joined: 08/26/2003 - 09:00

I think we all want clear answers on 'what exactly is it my child is allergic to'. But I am finding lots of us rarely get that answer.
Megan reacted to peanut/tree nut, egg, milk, and soy. We found these out by her reactions. She tested negative on RAST for everything. She skin tested positive for wheat, borderline positive to peanuts and fish. She also tested positive to dog, mold, dust mite, and ragweed....we have yet to see any reactions from any of those--but were given extensive instructions on how to control the dust mites in our home, etc.
Meanwhile, she was breaking out in hives everytime she had milk--yet it was negative. We think the fish was a false positive, but avoid it just in case for now. Her worst reactions were to peanuts/tree nuts. She was reacting to it being passed through breastmilk only (never had any firsthand) with vomitting, stomach cramps.... The wheat turned out to be on-track, and we hadn't suspected it (her reactions were different--runny nose/stuffed nose/slight stomach cramps/gas.
I am very frustrated with the allergists we have seen so far. I wish it were as simple as I want it to be...yes, she can eat these foods...these are the ones she is allergic to. I figured seeing the allergist would take the guess work out on my part. One allergist told me the only true test is eating the food and seeing the reaction. No test is 100% except for that.
Luckily, Megan's food allergies are not life-threatening (although I know the peanut allergy has the potential...we watch that one very closely!!)
I finally had to let go a little. For now, if Megan has reacted to a food, or tested postive--it is out of her diet. She has been allergen-free for over a year. My plan is to wait until she is older to really try some of the foods in her diet--until she can tell me better what's going on (my tummy hurts, my eyes itch, etc.). We will do more tests on fish and peanut/nut before she gets ready for school. If they are negative, then we will do a food challenge in the allergists office--and keep an epi-pen in the meantime.....just in case!
Hope this helps you know you are not alone in getting conflicting tests....it is very frustrating!!

Posted on: Tue, 03/30/2004 - 2:53am
LaurensMom's picture
Joined: 05/23/2001 - 09:00

My PA DD got negative results back from a RAST test. The allergist was new to us so unfamiliar with her history. When I questioned the results, he repeated test at another lab with same blood sample (yes, sure of this), which came back higher than what we believed her to be.
I demanded an explanation and he told me, "Labratories do not have a single standard by which they calibrate their equipment. Therefore, a RAST result of 4 might be 6 from another lab, which might be a 1 from another lab...That is why it is recommended that PA individuals treat their PA based on their reaction history rather than worrying about RAST results."
I was infuriated. What if this was the first time she had seen an allergist but we suspected the allergy. We wouldn't have even known enought to question and it could have been the difference between life and death.
Anyway, that might explain why the results do not match.

Posted on: Tue, 03/30/2004 - 2:46pm
ks65's picture
Joined: 03/06/2002 - 09:00

With the CAP RAST the results should not be different from lab to lab. It is actually called the Immunocap test (we call it CAP RAST here on the Boards) and it is the gold standard. It is a test that was developed or maybe trademarked by Pharmacia with very definitely parameters,etc. Apparently, the old "RAST" test was very unreliable and did vary from lab to lab and could be wrong...but this test is supposedly correct a very high percentage of the time. Anyhow, we are now always going to get the CAP RAST, but even with that...the results don't seem to make sense.


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