How Doctors Test Your Child for Food Allergies
Guest Post By Meenal Lele, Mom and Founder of Lil-Mixins
I remember when our pediatrician first suspected our son of having a food allergy. He was having eczema that wouldn't resolve, so I started doing some research on food allergy testing.
I was beyond dismayed to learn that in food allergy testing, the false positive rate is over 50%. That means 50-60% of positive results are not real!
What’s the point of a test that is wrong at least half of the time?
And yet, when a food allergy is suspected, the first step is often an allergy test, specifically what is known as a skin-prick test or sometimes, IgE blood testing.
So, should you drag your child to the allergist to undergo an uncomfortable skin prick session, or not? Here's a quick introduction to food allergy testing.
Things to Remember About Food Allergies
An important thing to remember is that as a general rule, food allergies are not sneaky. If symptoms show up after eating a food, then you might have an allergy.
Conversely, if you can sometimes eat the food, or if your child can eat a food without hives/anaphylaxis vomiting or other highly noticeable symptoms, there’s probably no allergy, and maybe no intolerance either.
In the end, eating a food and seeing a reaction is the only true way to confirm a food allergy.
But there are a few good reasons to go ahead with the skin prick testing or IgE blood testing:
Both can, with high certainty, rule out an allergy. If it’s negative, there’s almost definitely no allergy
Both can help differentiate a food intolerance, which is non-immunologic, and therefore not IgE mediated, from a food allergy
If there is a suspected allergy based on past history, then the tests can help confirm that
As a parent, there’s a strong urge to “just test them for everything.” But a lot of doctors recommend against that because of the high rates of false signals (also called false positives). An IgE sensitization is not the same as having an allergy. You may end up taking a bunch of foods out of your child’s diet for no reason.
What to Expect with IgE Testing
In skin prick testing, the doctor will place a drop of liquid containing the allergenic protein on the skin and then push down to prick through the top layer of skin. If your body already has the specific IgE antibody for that particular allergen, you’ll see a red puffy welt start to appear around that prick within fifteen minutes. After looking for welts and measuring the size, the doctor will wipe the area clean and apply a cortisone cream to stop any itching.
Our son's first skin prick test at the doctor's office
For IgE specific blood testing, a tube of blood is taken. The blood is sent to a lab where allergenic proteins are introduced to the blood, and the levels of specific IgE antibodies that show up are measured.
You’ll get a result for each allergen tested that from 0-100 kg/ IL. Higher scores in general mean more immune reaction, so a high score would likely indicate an allergy.
However you should not interpret the results without consulting a doctor. Different levels actually mean different things for each allergen, and it is quite common to see mildly elevated results all around in children who have other conditions such as eczema, asthma, or seasonal allergies.
We saw this with our son when he was first diagnosed and his eczema was not controlled. When the test was repeated a year later, all the values went down significantly across the board.
The printout showing our son's IgE blood test results
Oral Food Challenges
A doctor supervised oral food challenge is the one definitive test of a food allergy. This test is commonly used when it seems like someone may have outgrown a food allergy, based on IgE testing. Generally speaking, you will go to the doctor’s office and eat increasingly large amounts of the suspected allergen. This process takes four hours, so come prepared!
Our son doing his oral food challenge with syrup covered french toast
Once you have eaten a certain amount of the protein, you are considered to tolerate that allergen and therefore do not have an allergy. Why is it important to do this at a doctor’s office? Because a reaction can come on fast and you want to be right there with help if needed.
What About Home Food Allergy Test Kits?
These days, because my search history is all about food allergies, I see a lot of advertisements online for home-based food allergy or food intolerance screening tests.
I've done a bunch of research, and as far as I’ve been able to find, none of these diagnostic tests have been cleared by the FDA. That means that they have never created and presented data showing that their tests work.
Also, acupuncture, hair/urine testing, and any other such testing you may have heard of is also not proven.
When it comes to food allergies, it's important to focus on science-based testing and interpretation of results.
Hopefully this introduction to food allergy testing will be useful to you. If you have any further questions, definitely reach out to your child's pediatrician to get specific answers by a trained medical professional.
Remember that food allergy testing doesn't have to be stressful, and with proper care and management, you will pull through this uncertain period, just like we did.
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