Allergy testing: When to Use It and When to Not

As food allergies have gotten more common, more parents than ever want testing. There are definitely reasons to test, but testing can be expensive, and not all tests are equal. There are also differences between food allergies and food insensitivities. A true allergy occurs when the immune system reacts to something that really is not a threat, but causes measurable symptoms.

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Food allergies are reaction to food proteins because the body's immune system is reacting to something that really shouldn't be a threat. They are different from food insensitivities or intolerances, such as diarrhea and gas from lactose intolerance or red cheeks after eating tomato sauce.

There are three main types of food allergies: immunoglobulin E (IgE)–mediated (immediate) reactions, non–IgE-mediated (delayed) hypersensitivity reactions, and mixed reactions. IgE-mediated reactions are the type we often think about when we hear about a food allergy-- hives, itchy skin, wheezing, vomiting, throat swelling, and anaphylaxis. These reactions can occur immediately following exposure. Non-IgE-mediated allergic reactions can cause localized or generalized reactions, such as a skin rash or stomach upset, or even Celiac disease. Some allergic disorders have components of both IgE and non-IgE mediated types, such as eczema.

Determining if there is a food allergy requires both a history of symptoms with exposure and confirmation testing. In general, there are two different types of allergy testing. Children and adults can be tested by either method, depending on symptoms and other considerations. Both types of testing can lead to false positive results, meaning there is a reaction that makes a person look allergic to that trigger, but they really aren't. That means we have to look at symptoms along with the tests. No one should undergo testing "just to know" if there really aren't specific symptoms to evaluate. This can lead to overestimation of allergies, which can result in patients being on a severely restricted diet and lead to nutritional deficiencies. It also uses healthcare resources inappropriately and drives up healthcare costs.

Available testing:

• The first step is a careful history of exposures and symptoms. This may include a food elimination diet to help diagnose allergies.  
• Skin testing involves scratching a small amount of suspected allergens onto the skin or injecting a small amount of allergen into the skin. It is typically done in an allergist office, though some primary care doctors will offer it. (If you do this type, be sure the doctor has adequate training and does it routinely-- it requires a lot of expertise!) Results are generally known within minutes, based on local reactions to the various allergen areas. It can be uncomfortable for children, but many tolerate it just fine. This type of testing is often less expensive than blood panels. Patients must be off of their allergy medicines for this type of testing, which can be difficult for some severely allergic people. It can also be difficult in people with extensive eczema or other skin conditions. 
• Blood testing involves drawing a sample of blood and running many tests on a single sample. This may be preferred in children who cannot tolerate being off their allergy medicines (they can stay on medicines before testing blood) or in those who will not tolerate multiple skin scratches for the skin testing. It is generally more expensive than the skin testing and results can take a week or so to learn results. Blood tests that are recommended for allergy testing involve testing IgE, one of our immunoglobins that triggers allergy symptoms. There are health care providers who recommend IgG testing for food allergies. These are NOT proven to be of benefit. More on that below.   
• Oral challenges (giving the suspected food to the person and watching for a reaction) is often the best test for food allergies, but obviously can be very risky and should only be done in an experienced doctor's office.

Our website has information on the testing we offer from our office on the Allergy Test Results page. I don't want to duplicate all of that information here.

The driving force to write this post is the number of patients who come to me requesting that I order tests that were recommended by another healthcare provider. I always refuse to order tests that I do not think are indicated or worth while. It is difficult in the space of an office visit to go into all the details of why we don't want to order the labs, but a simple "they aren't recommended" doesn't sit well with families when they have their hopes set on finding answers. Insurance rarely covers non-proven tests, so if you're warned that insurance might not cover testing, that is a red flag that you should investigate further.

What are some of the tests that are not recommended?

There are medical providers who will order IgG panels for food allergies. This is simply not an appropriate test. Both allergic and non-allergic people will have IgG antibodies. They are the normal antibodies used to fight off infections and it is thought that when a food is eaten, the body makes IgG antibodies as a normal response. When food allergic people have been in clinical trials to desensitize their food allergies with immunotherapy, the IgG levels actually go up, despite lessening of clinical symptoms. IgG antibodies show exposure to foods—not allergy. For this reason most people who are tested react to MANY foods and are erroneously told they are allergic to those foods. This severely restricts the foods they are told are safe to eat. I worry that kids will suffer from nutritional deficiencies with such restricted diets. Of course, many of the providers who offer this testing also sell nutritional supplements, so they make money from the "allergies"... Think about it awhile. Do they really care if the test is valid or not? They know the numbers look convincing. They also know the more a person reacts to, the more money is to be made. Maybe they really believe in the tests and their procedures. Maybe they feel it helps. I don't agree and neither do the studies.

Hair analysis is another test that some people will recommend to look for allergies. It simply isn't helpful. At all.

I've had a few patients who have been tested by holding the food while the "specialist" measures arm strength. Supposedly if they are weakened by holding the food they are allergic to it. This is called applied kinesiology and has not been shown to help at all in identifying allergies.

People will take your money. They are usually good sales people. They will claim that labs can't lie and it is based on science. Ask to see the research. Learn to evaluate research first, because sometimes they will show fancy graphs that don't really support anything. But they look impressive. Beware! For some information on how to help learn to be a good judge of whether information is scientifically valid or not, see some of the links below.

Want to learn more? There is a lot of information available!

• More about how blood tests work and why they have false positives: Foodallergy.org 
• More on how skin prick testing works and why they have false positives: Foodallergy.org
• More on IgE testing: ScienceBasedMedicine.org
• More on other unproven diagnostic tests: FoodAllergy.org
• Guidelines for the Diagnosis and Management of Food Allergy in the United States is a comprehensive summary for patients and parents of the guidelines outlining testing for as well as management of allergies. It is important to note that it was published in 2011. (I can't find an update.) The recommendations for influenza vaccine for those with egg allergy has changed since then. It is now recommended to give the influenza vaccine despite an egg allergy. For more information on egg allergy and influenza vaccine, see this update.
• Want to know if what you're reading on the internet is reliable? Take this quick tutorial from the National Library of Medicine. It's free and only takes about 15 minutes!
• Still want to learn more about how to evaluate science? Take a look a the many resources on www.ScienceOrNot.net.