The Cost of False Positives

Guys. Food allergy testing is the worst. Mainly because the only way to know if you (or your kid) is actually allergic to something is to eat it and see what happens. I call this the "mess around and find out method". That's crazy. With how much we know about the human body and the immune system, the only way we can definitely say, "Hey, you are allergic to this" is to give it to you and make you have an allergic reaction. 

Because of what happens during a positive oral food challenge, skin tests are the usually the first stop for an allergist. I’ve talked about them before- the nurse scratches your skin with things you might be allergic to and they measure the response after waiting 20 minutes. Today, I'm going to talk (vent) about the main problem with skin tests- that they have a 50% false positive rate. This means that if you have a positive skin test (your skin is red, itchy, and swells up), 50% of the time you can eat that food no problem! Take that in for a second. One out of every two people who react to having their skin scratched with a food can eat that food without risk of an allergic reaction. And there’s research on how big the swelling is and how likely it is that it’s safe to eat, but really, there’s just no way to know unless you actually eat it.

What does this mean? Well, for us it means we have been avoiding garlic for TWO YEARS and we have no idea if my kid is actually allergic. Two years of making my own pasta sauce. Spice mixes. Pesto. Hummus. Ranch. Avoiding anything other than plain crackers. Only eating plain chips. Meticulously reading every ingredient on lunch meat. Only eating one brand of chicken nuggets. For TWO YEARS.

And okay, if she is allergic to garlic, then I’ve done a lot of work in the kitchen and I’ve kept her safe and I can feel good about that.

But if she’s not allergic to garlic (because really, who’s actually really, truly allergic allergic to garlic?) then I have been working as a personal chef for FREE for NO REASON for TWO YEARS.

One thing that I see a lot on food allergy twitter is to not use skin tests as a screening process for food allergies. With so many false positives, you shouldn’t just go looking for allergies when there’s no good reason to. At best all you are going to do is make families unnecessarily avoid foods and at worst you could miss the window to introduce that food and actually cause an allergy/intolerance/aversion.

At first, the decision to avoid garlic was pretty easy- after one round of unexplained anaphylaxis, I would do ANYTHING to avoid it happening again.

To be fair, our allergist didn’t just go looking for a rare garlic allergy, our kid had anaphylaxis and we didn’t know what to. At first we thought that our garlic sauce had somehow gotten into her food. She had negative skin tests to milk (what she was eating) and shellfish (what we were eating). So what else could it be? But when she had anaphylaxis again (again eating milk), it became clear that the garlic we were eating at nothing to do with her reaction. But the damage had been done- we are stuck with her skin reaction to garlic being so large, our allergist is afraid to let her try it. 

Now, the scales have tipped. What actually is her risk of anaphylaxis from garlic? 50%? And what I thought would be a slight inconvenience has become something that has completely changed my life. My weekly meal planning is consumed by avoiding food allergens.

Just let her try it! We’ll never know if she’s actually allergic! I don’t think our allergist really understands what a burden avoiding garlic is. It is IN EVERYTHING. It’s easy enough to leave out of things you make from scratch, but garlic is in EVERYTHING. EVERYTHING. And it may be all for nothing! I don't want want her to have anaphylaxis. I really don't. But, I really want her to be able to eat all the food she can safely have.