Why do a blood/allergy testing if they are not reliable?

[monkeybum]

I've read and been told by an allergist that tests have a 50/50 false-negative and false-positive rate. So why do them?

If there is a 50/50 chance they are wrong and the answer is the opposite, what does it tell you if you do one?

She told me this about blood and scratch tests. I asked her why bother then, and she got all flustered and said the test results had to be looked at in conjunction with results of an oral challenge, and that an oral challenge was the only true way to know if you have an allergy. I'm surprised she would say this as she was basically telling me that what she did for a living was useless...

Also, I understand that you can be allergic to something on a test, but only end up with a very very mild reaction or no reaction, and really can eat it without problems. I know people who've done testing and been told they are allergic to things they've always eaten without problems, but now they avoid them. Do you really need to eliminate something from your diet if you can eat it without problems?

Are there more reliable ways to detect problematic allergies other than oral challenges?

[kjbrown92]

My kids have done intradermal testing (which is supposed to be a little more accurate than scratch testing; three graduated doses of an allergen are injected under the skin). And my kids had intolerance testing through ALCAT. I did the allergy testing basically to rule out allergies (because I knew they had food issues, but I didn't know which kind they were: allergies or intolerances). I believe that RAST (blood test) is less accurate than a scratch test. Not sure what the accuracy is of patch testing.

[Therese's Mommy]

Well, when dealing with a child I like to err on the side of caution. So, if she tests positive we will avoid it instead of doing an oral challenge at this time. Also, our allergist uses the SPT and RAST together. For instance, originally dd tested neg via SPT for an egg allergy. DD refused to eat eggs so we did a RAST and it came back pretty highly pos. A year passed and we redid the RAST. Her egg number had dropped from 7.48 to .5. Her allergist wanted to wait another 6mos and then do an in office challenge. Before doing the challenge she did a SPT to try and confirm what she was seeing on the RAST. Unfortunately, her SPT came back positive, so we didn't do the challenge.

It is my understanding that tests are a little more accurate for adults. Supposed there were 5 things you suspected. You could be tested for those 5 and if one comes back pos you could be fairly certain that is the problem. Eliminate it, but keep eating the rest and see what happens. So, imo, testing does serve a purpose but has to be used in conjunction with other things.

[SpottedFoxx]

Because for one, it's a starting point. Like the brain, allergies are really one of the unknowns - it doesn't mean a brain surgeon's profession is useless. It just means that there is a great deal about our allergy response system that doctors just don't know yet.

[scsigrl]

It is very frustrating to not get 100% results but as others have said it can be a "jumping off" point.

I did 2 dairy trials when DS was 6 and 9 months old. Nothing changed so I went back to eating it. At 13 months we tried eggs with a really bad reaction. Same with milk. Took him for SPT's and found a LONG lost of allergies. I cut them and within 3 days he was sleeping through the night. He has also had RAST testing and confirmed the SKP but also showed some differences as well.

It gives some ideas of what might be going on.

[sbgrace]

If you're talking about IGE allergies negative results are pretty reliable. This isn't testing for intolerances or IGG stuff.

The positives are 50/50. So if you're positive and you suspected the food due to reactions you're likely allergic. If you're positive and there is question you do a food challenge to see if there truly is an allergy. But if you're negative you're likely not allergic. So allergy testing is good for narrowing down the possibilities.

Example: My son had a serious reaction to a dessert. We had question about what the issue was between blackberries and walnuts. He was negative to both of them in allergy testing but he was positive to six other tree nuts. So we could assume his serious reaction was to cross contamination of the walnuts in the dessert he had with another nut. I wouldn't hesitate to feed him blackberry. I pray he never consumes another nut.