I know that skin tests tend to be prone to false positives, but anyone have experience with false negatives?
My ten year old is allergic to milk, egg, peanut, tree nut, and mustard. At his skin test last week, we were shocked to see him test negative to peanuts. All of his other allergens were definite positives. Last year, his peanut skin test was 15/30- that's on the smaller side for him, but definitely not anything borderline. His RAST for peanuts was 16.2. We redid the RAST, obviously, and are betting on some bizarre fluke, but it's hard not to get excited about the possibility of maybe outgrowing something.
I'd appreciate any thoughts or experiences...
I have false negatives to all my allergens on the skin test, despite contact hive reactions outside of the allergist's office. I had false positives on the same test. My Mum has false negatives to two of her three food allergens too, thogh no contact reactions for her otherwise. So it happens. I think the statistic I last read was false negatives can happen in up to 10% of patients. That is pretty high when you think of it. I don't know if that rate is for people who repeatedly test false negative or if it includes those who tested positive one time and then no wheal another time. Hopefully someone with more experience will chime in.
It will be interesting to see the new RAST scores to see if they reflect a lower number as well. I hope you can get some answers from your allergist.
Thank you! I really doubt he has outgrown it, but am anxiously awaiting the blood test to see where that stands.
RAST came back- he has definitely not outgrown.
Younger DS had false negative to dairy when he was little, and the allergist was clear that the test results aren't 100%, which is why a clinical history is so important.
DD also skin tests negative to milk-- and she shouldn't. Well, at least in the past.
She also skin tests negative for almond now, but I'm not sure that I'll believe that one without an IOFC, either.
The false negative rate (according to our own Dr. Awesome) is a bit under 5%-- that is, for those people who genuinely HAVE an IgE-mediated food allergy, as many as 5% of those people could skin test negative at any particular time, for reasons that aren't clear.
I'm not sure where his value comes from. It's definitely that testing negative is WAY more meaningful than testing positive-- and that SPT which are negative are more meaningful by far than RAST which are-- but it's not foolproof.