blood vs. skin test


maybe someone can shead some light here for me. A little backgound. My 2 1/2 year old had a milk allergy that she grew out of. We have had a few tests for milk and peanut. One at 12 months, peanut came negative in blood. I gave her some peanut butter at about 18 months since I was assured she did not have a peanut allergy, she had a mild reaction. HIves that went away with benedryl in about 20 minutes. We then got her another blood and skin test again blood came negative and skin came up positive. Again at 2 1/2 skin came up positive. So my question is what is the difference in skin and RAST testing. Why is her blood coming up negative. I believe her allergy does exisit becasue I seen her have a rewaction to it but confused about the different testing. When I asked her allergist he said "oh sometimes that happens" HUH? what does that mean? THANKS

On Nov 8, 2007

I recently listened to a leading allergist speak of this , when tests come up negative they give and oral challenge, that is what you need to listen to , not the blood test, she failed an oral challenge per say as you tried and she reacted. It is such a tricky science and all doctors feel differently,, my allergist based on the reaction of her prick test (size) commented to my family doctor that her prick test reaction was severe so we should use all cautions, avoidence, and epi. Peanut allergies are very unpredictable.Use more caution than less and do not feed her without immediate access to EPI that is my educated suggestion. That means the blood tests as well as all allergy tests can have false results .

On Nov 8, 2007

thank you. That makes sence. We know her allergy exists and we are a peanut free house and have an epi. we do not give her ANY peanut products. I was juts curious in the testing and how it is determined. You had a great point, she failed an "oral challenge" so obviously the allergy is there. I had given her PB before and that was her first reaction. It is very tricky. Thanks for the info. that made lots of sense to me!

On Nov 8, 2007

I hope your little one has no allergies , I have one with and one without . Good luck to you , safe eating.