FOOD ALLERGY TESTING
Food allergy testing is used to find out if you or your child has an allergy to a specific food.
Food allergy reactions can include hives, redness, swelling, vomiting, diarrhea, GI pain, coughing, wheezing, runny nose, itchy eyes, throat swelling, or some other symptoms. When these occur, it’s definitely cause for concern.
WHY DO FOOD ALLERGY TESTS?
Food allergy testing may provide answers to which foods you are allergic to and should avoid.
WHICH TESTS ARE USED TO DIAGNOSE FOOD ALLERGY?
There are 3 diagnostic tests for IgE mediated food allergies. Together with reaction history, an accurate diagnosis of what you are allergic to can be determined.
2 important points to note about skin and blood tests:
- High rate of false positives
- Cannot determine severity of reaction
Read Dr. David Stukus’ What You Need to Know About Food Allergy Testing.
If you’re preparing to do an Oral Food Challenge (OFC) at your doctor’s office, here’s some advice on How to Prepare for an Oral Food Challenge.
For my older son, it happened when he was 2 years old. He had tried milk and soy milk many times, why not try almond milk? So there we sat having crackers and almond milk, then the redness and hives started. I didn’t know anything about food allergies at the time.
We saw an allergist, managed to get through a very long 15 minute skin test to see what he was allergic to, was given a prescription for epinephrine, and sent on our way. The allergist recommended us to avoid all the offending foods on the skin test. That was the start of a new chapter in our life.
For my younger daughter, it happened when she was about 10 months old. She had been exclusively breastfed since birth. She had caught a cold and seemed to need more fluids which I wasn’t able to produce. So I mixed up some powdered formula (Enfamil) which she downed excitedly. She definitely was thirsty!
Over the coming week, she had explosive diarrhea. I called it that because it went up her diaper and onto her back multiple times a day. She needed a bath after each episode! We couldn’t leave the house. Who knew that this was an allergic reaction? I didn’t. The allergist recommended strict avoidance of milk. Interestingly, my diet included dairy all this time I was nursing her and she seemed to be fine. If there was some other subtle symptom (perhaps eczema), I didn’t connect it.
ALLERGIC TO SOMETHING YOU ATE?
Different foods can cause reactions of different severity, so you can definitely be more allergic to one food than another. Since we eat so many different foods in a day, it’s sometimes difficult to tell exactly which food is the culprit.
To get a better idea, try keeping track of all the foods your child eats for several weeks to see if you notice a pattern. Whether it’s hives, redness, swelling, vomiting, diarrhea, GI pain, coughing, wheezing, runny nose, itchy eyes, throat swelling, or some other symptom, keep track of it and see if it relates to any specific foods.
If you keep a food diary, you’ll be better prepared for your appointment with an allergist. You’ll be able to discuss what you may have discovered in the past weeks from your diary and what the next steps might be. Definitely bring your diary with you so you can go over it with your allergist. He will be able to offer more insight.
HOW IS FOOD ALLERGY TESTING DONE?
Before any testing can be done, all antihistamines need to be completely out of your system so that you can get more accurate results. Antihistamines block histamines and can relieve allergy symptoms. You’ll need to be off antihistamines for at least 5 days. Popular antihistamines can include Zyrtec, Benadryl, Claritin, Allegra, Hydroxyzine, some prescription eye drops and nasal sprays, among others. This list is not all-inclusive.
SKIN PRICK TEST
Allergists usually recommend a Skin Prick Test (SPT) as a first step. This is done in the allergist’s office on the forearm or back. Each allergen is introduced onto the skin by slightly scratching the surface with a small plastic probe dipped in a solution containing the food allergen. It feels like a fingernail scratch and is not painful.
However, it can be very itchy and hard to stay still. It would be wise to bring something to distract the child so he doesn’t scratch the test area, perhaps a favorite video to watch on your iPad.
After 15 minutes, the allergist examines and measures the reaction, if any. If there’s a suspected allergy, there will be redness and raised swelling that may resemble a mosquito bite. The skin prick test is less costly and easy to do, however, there is a high rate of false positives (50-60%). Skin testing can only really confirm what you’re not allergic to. Everything else will require additional testing. Unfortunately with so many variables, food allergy testing is not an exact science.
The second step would be to get your blood tested. When you test positive for a food allergy in a skin test, your blood test may or may not show an allergy. So it’s a good idea to test all the foods that were positive in the skin test.
The blood test is a more accurate test than the Skin Prick Test and is called the Specific IgE test or RAST. It measures the IgE antibody levels in the blood that are specific to different allergens or foods. That was a mouthful, I know! Basically, given what you know from the skin test, you can request specific allergens (foods) be tested with your blood to see how it reacts.
For example, if you choose the nut panel, your blood will be tested against all the different nuts listed for this panel. Your results will show the IgE level for each nut. The higher the number, the more allergic you may be to that specific nut.
This test is more expensive to administer and involves a blood draw in the lab. Depending on the age of the person with the suspected allergies, this may or may not be an option for you at this time. Some allergists do not recommend the RAST blood test until they reach a certain age.
ORAL FOOD CHALLENGE
Given the results of your skin and blood tests, you may want to take it a step further to confirm a non-allergenic food or a suspected food allergy with an Oral Food Challenge. This should only be done in a doctor’s office, NOT at home.
Really, a food challenge is the only sure fire way to know whether you are really allergic to a certain food or not. The skin and blood tests try to simulate the reaction in your body, but to really know, you’ll need to eat that food.
Don’t do this at home! You never know what allergic reaction may happen, and it can be potentially life threatening, so it’s best done with an allergist.
Some allergists offer food challenges in their office, but they must be scheduled far in advance as the appointments can take hours. Typically, the food being tested is given in tiny but increasing amounts with a wait period between each dose. You are kept under close observation by the allergist or nurses. After each increment, the dose is increased little by little. If an allergic reaction occurs at any time, the challenge would be stopped.
It’s important to bring in food for your challenge that is not contaminated with other foods. If you are doing a nut challenge, Nut-Free New York has a great resource for finding uncontaminated nuts.
Remember to bring in some toys, videos, iPad, books, etc. to keep you or your child busy during these few hours of waiting time. Also it’d be a good idea to bring in some treats in case you need to bribe your child to eat the challenge food. We brought cookies so my daughter had something to look forward to after each incremental dosage. It also served to get the taste out of her mouth. You might also want to bring in a meal just in case you get super hungry – it is after all, a couple hours.
If you pass your challenge, it’d be time for a celebration!
I hope this has given you some food for thought and an action plan on what to do next for a possible food allergy testing. It’s not the end of the world, as I always say. Many people live a safe and healthy life with food allergies. There are also many new treatments in the works at allergy research centers.
Once you have your testing results, you might like to read about how we keep our kids with food allergies safe in everyday life.
What has worked for you? If you have advice, please share in the comments. We’d love to hear from you.
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