Skin testing vs blood testing???


Can anyone tell me which test is most reliable and is the most acurrate? I am really torn as to which test my daughter should get.

Also, is it true that testing before age 3 is not really reliable?

Thanks for all your input


On Jun 20, 2003

All I know is that our allergist wanted to do skin testing. I said no - I didn't want to expose him to any peanut. He acted like I was over-reacting. Then when the RAST tests came back so high - he recommended that I never have him skin tested. He then claimed that this was the last year he would of recommended the skin tests anyway (3 years old) that he thought the blood tests were too traumatic for 3 year olds or younger. But my guys have never been scared of needles - don't cry for shots or such. So I guess it's what ever you or your children are comfortable with.

I don't know about reliability of one versus the other.

------------------ Sherlyn Mom to 3 year old twins Ben & Mike - one PA & the other not. Stay Informed And Peanut Free!

On Jun 20, 2003

Hi Gwen.

Based upon what I have learned from my daughter's allergist, I would definitely NOT give your 2 1/2 year old a skin test for several reasons:

(1) Children whose older sibling has a food allergy to avoid delay the introduction of ALL major allergens as follows:

wheat/soy/milk - 12 months egg- 18 months peanuts, tree nuts, fish and shellfish - 3-4 years

My DD's allergist says that if you follow this protocol (including avoidance of may contains), your child's chances of being allergy-free are very good.

It stands to reason then that if you give your child a skin test, this would count as an exposure -- and could possibly make him/her more likely to become allergic.

(2) There is a relatively high false positive rate associated with skin tests. CAP-RAST are the most reliable (next to the oral food challenge itself).

(3) I asked my daughter's allergist specifically if he could test my 2 year old sooner. I, too, wanted the peace of mind of knowing whether she would be allergic before starting preschool. He said there is simply no way you can test a child before 3 to know this with any certainty.

I would definitely question your allergist about this further. I think there's a lot of ignorance out there, even among so-called "board certified specialists" and we, as the parents, really need to make sure we educate ourselves instead of blindly trusting the doctors to make potentially life-altering decisions for us and our children.

Good luck.

[This message has been edited by Kami's Mom (edited June 25, 2003).]

On Jun 21, 2003

Hi Kami's Mom,

Thanks so much for your mdetailed message- I am really going to re-think this and am probably not going to have her skin tested.

She will be 3 in October- should I do the Cap-Rast test at this time?? Is this just the blood test??

On Jun 21, 2003

I first had my daughter skin tested at 2 years, then at 4 and 5 1/2. Each time, the reaction was bigger than the last time. My allergist said that he will not test her again - that each time counted as an "exposure" and that each subsequent test may have contributed to her bigger reaction - I wonder if he knew this when she was 2 - I get the impression that our doctors are learning as they go along just as we are.

On Jun 21, 2003

You're welcome Gwen. The CAP-RAST is a blood test that measures the level of IgE antibody for a specific allergen in the blood. If you get it done, the lab can test for numerous allergens with just one blood sample.

However, be sure not to confuse the CAP-RAST test with the RAST test (also a blood test). The CAP-RAST is the preferred, newer version.

I won't be testing my younger daughter until May 2004, soon after she turns 3.

On Jun 21, 2003

My daughter was skin tested (that's when I found out her allergy info), but should I request to get the CAP RAST? What more info would it give me; would it tell me how allergic she is (other than 4++)? What else will it do? How much blood do you need?

New to this!thanks!

On Jun 22, 2003

Our allergist recommended at Cap Rast at 18 months. It came back as negative yet she had full body hives with an exposure to peanut butter. I would agree that testing before age 3 doesn't do any good. We are going to have her tested again when she reaches 3.

On Jun 23, 2003

My daughter had a reaction to peanuts at 20 months old. Actually, she also reacted to peanut oil in sunscreen at 8 months old. I had her skin tested at age 2 and she was 4++. The only reason we did the skin test was to confirm what we already knew (my son is also PA) and get an EpiPen, Jr. The allergist said that she doesn't think a CAP RAST is necessary at this time, and that when she is over 3, we can do further testing for other potential allergens and possibly the CAP RAST for peanuts at that time.

I take this to mean that she doesn't think the testing before 3 is reliable, but she did not say as much. That was just my take on it, but regardless, I know my DD is PA as she has reacted.


[This message has been edited by MeCash (edited June 23, 2003).]

On Jun 23, 2003

Just want to clarify something: I believe that Gwen's original question concerned testing her NOT-YET-ALLERGIC younger child -- one that has never had a known reaction -- to see if she is allergic.

My response to her about the futility of testing those younger than 3 was referring only to children who have never had a reaction and had never been exposed to the particular allergen being tested.

I don't think it would be correct to assume that this would apply to children younger than three who are being tested for an obvious reaction.

On Jun 24, 2003


I have to ask you if the CAP RAST is more preferred why did Dr. Wood do a RAST on my daughter who is severely PA and suggest doing a RAST for tree nuts on my other DD also severely pa?

I have been told by 2 allergists the RAST is preferred.... that the CAP RAST is for those unclear results.

On Jun 24, 2003

My ped ordered a RAST for my 22 mo old dd after a topical reaction to peanuts. Then we went to see the allergist, he wanted a CAP RAST done. Although I didn't want to put her through the horror of another blood draw, I understood the benefits.

Versus RAST, he claims that it is more consistent from lab to lab and that the result is more conclusive and predictive. If a low score on the CAP RAST the higher chance of growing out of it. And if under 15, there is only a 98% chance of having a severe reaction. My dd scored a 5 on the RAST (0-6 range) and >100 on the CAP RAST which is only scored 0-100 (6 levels within that). Based on her high score, he then suggested that we should not her be in an enclosed environment with peanuts as she might react to the proteins in the air.

Here's a link to one website comparing the 2 [url=""][/url]

And here's another comparing the reliability of the tests [url=""][/url]

[This message has been edited by Driving Me Nutty (edited June 25, 2003).]

On Jun 25, 2003

I am new to this board and am upset about the skin vs blood test. My ds at 1years old was skin tested and was positive for peanuts. So, does that mean he may never outgrow this allergy? I read that 20% of kids do outgrow the peanut allergy (or am I being optimistic?) Has anyone outgrown peanut allergies that you know of?

On Jun 25, 2003

Kami Mom,

You are right I am asking about my dd who will be 3 in Oct. of this year. My older dd is PA/TN allergic. My younger one has not been exposed, nor reacted to any PA products.

I want to get her tested as she will start preschool in the fall and I feel like we need to know.

I am not sure I have figured out the answer based on the replies though.

The allergist say's skin testing is the most accurate, but I don't want to have that be an exposure for her. Does it sound like the CAP-RAST is the way to go???

Thanks for everything,


On Jun 25, 2003

Hi Westporter -- Yes there is research that states that certain children can outgrow their PA. Typically those that have been shown to outgrow it are diagnosed fairly young, absolutely avoid the allergen (including cross-contaminated food, like "may contains"), and do not have asthma.

And yes, I know someone who outgrew the allergy -- my 5 year old daughter!

HOWEVER, there is also research showing some children can get the allergy back. And that is the fear that I am living with right now.

Since you are new the the PA, there's a lot to learn. There's a wealth of information on this site, so please educate yourself. As you will find, not all allergists are as educated as some of the people on this board!

Did you have your 1-year old tested because of a reaction?

Gwen's Mom - As I mentioned in my previous post, Dr. Wood says that there is nothing you can learn by testing an unexposed child who is less than three. I would wait until she turns three. I am facing the exact same issue with my 2 1/2 year old. Basically, I have told the preschool the situation -- that she is to eat no food unless I have provided it or preapproved it. Then hopefully when she turns 3 (and tests negative!) we won't have to worry.

Samirosenjacken -- Don't know why Dr. Wood did a RAST instead of a CAP-RAST. Everything he has told me indicates the CAP-RAST is the ultimate test.

[This message has been edited by Kami's Mom (edited June 25, 2003).]

On Jun 25, 2003

Hi Kami's mom,

My son (now 16 months old) went to an allergist because I thought he was allergic to milk. He is allergic to milk, egg & peanuts. I never had given him any form of peanuts prior to that knowing not to give him any til age 3.

I strongly believe (and feel quite guilty about it) that I gave him the peanut allergy. When I was 28 weeks pregnant, I was diagnosed with gestational diabetes. On the food program I followed contained peanuts and peanut butter for protein among other foods. I ate peanut butter and/or peanuts every day for protein (in the morning, and 2 snacks) because I am not a big fan of cheese, etc for protein. I NEVER thought about peanut allergies, it didn't occur to me since I have never been around someone with it.

Anyhow, I asked my son's pediatrician why the peanut butter & peanuts were on the list that the hospital gave me and she said that its not known what causes the allergy. But, I am convinced that my eating it every day caused this. Plus, there is no mention in any of my pregnancy books to stay away from peanuts. Any thought on this forum members?

Congratulations that your child outgrew it. Also, should I join the peanut allergy group for $25? I am a member of FAAN.

Thanks for the input.

On Jun 25, 2003

Hey Westporter,

I know you feel guilty, but it's not your fault. You were only following the advice of medical professionals who should know better. Yes there are studies that show that sensitization can occur in the last trimester of pregnancy as well as through breastfeeding. It kills me that there seem to be no OBs or pediatricians who know about this. It's not until after our kids get the allergy that we find out all this stuff that we should have been doing.

About the skin test results: This excerpt is taken from a food allergy conference I attended last year as presented by Dr. Wood, a leading food allergist at Johns Hopkins:

"The problem with allergy testing is that there are a large number of inaccurate reults from both skin testing and blood testing...There are two main reasons for these false positive tests. First, it is possible to have enough IgE antibody to produce a positive allergy test but still be able to eat that food without difficulty. Second, when you are truly alergic to one food, it is common to have positive tests to other related foods..."

So when skin tests are not performed in response to an obvious reaction, I think their validity needs to be questioned.

I have been told that it is useless to test a child younger than 3 for a specific food allergy (unless of course that child has had a reaction). I don't know if this is because such a test on such a child may incorrectly show a positive result; or incorrectly show a negative result.

Given this information, perhaps there is hope that your child is not PA after all. And if the allergy is true, there is also hope that it could be outgrown.

Good luck!

[This message has been edited by Kami's Mom (edited June 25, 2003).]