“What to expect from allergy testing” 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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Note: This is the first of two posts on what to expect from allergy testing. The original draft got rather long, so I decided to split it up so as not to inundate you, gentle readers. (This is what happens when I listen to television show soundtracks while writing.)
I was never “tested” for allergies as a child. Most of my diagnoses in the 1970s and 1980s came more from guessing games made by a family doctor. Though, in his defense, allergy testing had been around for only roughly 100 years when I came into this world.
A little history
While allergic disorders appeared in Egyptian hieroglyphics for over 2000 years, the term “allergy” didn’t come into being until Von Pirquet coined the term around the beginning of the 20th century. The first known “test” for allergies occurred in 1869, when Dr. Charles Blakely used pollen on a wound to document the reaction and results.
But it wasn’t until the 1950s, after scientists discovered mast cells and how they helped cause immune responses to allergens. The concept of the body releasing histamines in response to allergic reactions was discovered in 1963.
Hmm…that’s less than 20 years before I was born. Maybe I should cut my old doctor some slack.
Mind you, those discoveries and tests were for environmental allergies. On the food allergy side, Carl Prausnitz and Heinz Küstner developed the Prausnitz-Küstner test in the 1921. This was the basis for the modern under-the-skin allergy testing we have today. Testing has continued to improve over the years, and now we have several different types of allergy tests.
Common allergy tests
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 a future post instead (because, unfortunately, the next post will talk about needles, too).
Skin and blood tests are more effective than the elimination diet at determining which common food allergies you have. Several of these tests take around 15 minutes after administration to receive results, while one of them can take 2-3 days to show results. Let’s take a look at these tests.
Scratch test
Also known as a “prick test” or “percutaneous test,” the scratch test involves pricking or scratching the skin and exposing it to a small drop of an allergen. This test can check for up to 50 different substances at once. There are versions for both food and environmental allergies, though most immunologists recommend not testing both types of allergies on the same day to prevent overloading the body’s immune system.
I went through both versions of this test. They weren’t fun, and I’m glad I did, because it finally answered questions I had been asking for years. However, one of my back prick tests caused enough of a reaction that the doctor gave me two different antihistamines and prescribed me an Epi-pen. I believe that was for the environmental allergy test, though, and it isn’t an experience I would wish on anyone else.
Intradermal test
The intradermal test is administered in the arm, instead of the back; doctors use this test when scratch tests are inconclusive. While immunologists commonly use this test to check for penicillin and insect venom reactions, my immunologist used it to confirm my milk and wheat allergies.
This one was even less fun than the previous one, and it was also worth it.
Patch test
While the scratch and intradermal tests check for internal allergic reactions (despite the fact that they show up on the skin, hives are considered an internal allergy), patch tests check for contact dermatitis, which is a skin inflammation reaction to allergens. Normally this is used to detect delayed allergic reactions and can be great for determining what causes your special brand of eczema.
There are about 20-30 substances that can cause contact dermatitis, and, while most of them are environmental, some substances like food preservatives and certain foods (like wheat) can also be culprits.
Blood (IgE) test
Blood (IgE) tests happen in a lab instead of the doctor’s office. Your doctor sends your blood sample to the lab, where technicians add allergens to the blood and record the immunoglobulin levels that develop. There are two types of Blood (IgE) tests: a total IgE test measures the IgE antibodies for all allergens, while a specific IgE test looks for the immunoglobulin response for one specific allergen.
Skin tests are more reliable than blood tests, but not everyone qualify for the skin tests, especially if they are taking antihistamines or have rashes or hives, which will affect the tests. In those cases, a blood test is necessary.
Oral challenge test
If skin and blood tests don’t product conclusive results, immunologists sometimes resort to the oral challenge test. Here they give the patient 4-6 doses of an allergen and wait about 15 minutes between each dose. The patient has an allergy if a reaction occurs and doesn’t if they take the full dosage and have no reaction.
Doctors perform oral challenge tests in three different ways:
- Double-blind – neither you nor your doctor know which dose is an allergen or placebo
- Single-blind – your doctor knows which dose is which
- Open-food – both of you know what you’re taking
Real talk time: This test requires medical supervision. Do not ever try to do this on your own or anywhere outside of a doctor’s office.
That’s all for today. Tune in next week for how to prepare, what to expect during, and how to incorporate the results from testing.
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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