“What to expect from allergy testing: Before, during, and after” Disclaimer: None of the information provided in these posts should be taken as medical advice. Please consult with your doctor before trying recommendations or if you have concern
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When you and your immunologist determine allergy testing is necessary, here are some things you can expect. In all of them, they will record your detailed medical history, including family history, and may perform a physical examination to look for clues regarding your reactions.
Trigger warning: We’re going to be talking about needles very soon, so please proceed with that in mind. If you need to stop reading, that’s okay. Tune in for my next post instead. As I mentioned in the last post, I didn’t get allergy tested until later in life. And, while I’m not afraid of needles, oof, there’s a lot of needles involved in allergy testing (well, in most of the tests).
How to prepare for a food allergy test
Regardless of the test type, your doctor may have you stop taking over-the-counter (OTC) or prescription antihistamines, and they will let you know how long you have to forego them before testing. However, do continue taking any antibiotics, asthma inhalers, or nose sprays.
Scratch, Intradermal, and Patch tests
- You can bathe beforehand, but avoid using lotions or body sprays, because those can affect the tests.
- Do not shower, swim, or participate in any activity that induces sweating for several days after a patch test.
Blood test
- Your immunologist may have you fast beforehand (usually similar to other fasting blood tests).
Oral challenge test
- Avoid any known allergens for at least 1-2 weeks before testing.
- Do not eat or drink before the test, unless you need to for another health reason; if so, eat as little as possible.
- Make sure you are not sick (if so, cancel and reschedule, especially if your asthma is acting up).
- Bring your (or your child’s) epinephrine pen with you in case of a reaction after you leave the office.
What happens during testing
Scratch test
Your doctor usually performs this one on the back, so you usually lie face-down on a table. A tech draws a grid on your back and uses individual needles to place a small amount of allergen to the squares; there is a different allergen in each square. Once all of the allergens are under the skin, this test takes about 15 minutes to create raised, red, itchy bumps called “wheals.” After the wait, they measure the wheals to see if the bumps are large enough to qualify as an allergic reaction. Afterwards, the technician administers a steroid to the back to stop itching, and the doctor can give you an antihistamine if the itching continues.
Intradermal test
A tech has you sit in a chair, and the doctor or tech administers the allergen dose (again, it’s small) under the skin This one involves injecting a small dose of allergen under the skin in the arm and waiting 15 minutes to see if any reactions occur.
Patch test
Here we have no needles (yay!). Instead, your doctor applies the allergen to your skin and covers it with a bandage, which you wear for 48 hours. Remember, you have to avoid bathing or activities that cause heavy sweating (that’s right, time to skip leg or arm day at the gym). Back at the doctor’s office, they remove the bandages and record any reactions that occur and determine whether they are allergic reactions.
Blood (IgE) test
Yeah, we’re back to needles (total sarcasm there). This is simply a blood draw (like you would get for standard bloodwork). Your doctor follows up with you once the test results are in.
Oral challenge
Your doctor has you bring in the food for your challenge and prescribes three to seven graded doses of the food you’re testing. Once you eat it, you wait about 15 minutes between doses, and your doctor monitors your reactions. If no reaction occurs after a dose, they administer a higher dose and continue monitoring. Expect to stay an hour after the last dose so see if you have a delayed reaction.
“False Positives”
No test is foolproof, and that includes allergy testing. Skin and blood tests can show what is known as a “false positive,” where the test shows a reaction that isn’t a reaction. Your body can produce antibodies to an allergen but never cause a reaction despite showing up on a test. This can cause the wheals to show up, but those wheals may be smaller and considered “borderline” allergens.
Frustrating? Yes.
I remember talking to my immunologist about this, and he explained that, sometimes, the overall across-the-board skin prick test can overload the system, causing reactions that aren’t necessarily reactions. For the false positive results, he had me avoid those foods for about 2-3 weeks and then reintroduce them one at a time and see if I reacted to any of them. If I reacted, I was allergic; if I did not react, I was in the clear. Talk with your immunologist about how they want to further test any possible false positives.
What next?
Once you have your results, your immunologist works with you to create a treatment plan. It might involve changing OTC or adding prescription antihistamines. They also advise you on how to identify and avoid any food allergens either themselves or through a trained nutritionist. Following this plan will help keep you as healthy as possible and, more importantly, safe.
That’s all for today. Tune in next week to learn about the elimination diet and how doctors use it to conduct allergy testing. I might also throw in a recipe or two you can use while on the diet.
If you have an allergy testing story to tell, go ahead and share it in the comments if you’re comfortable doing so. Everyone reacts differently, and I to hear your story.
Be safe. Eat safe. And savor life!
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