Testing for Food Allergies

all about allergy tests

If you think you might have food allergies, chances are, you’re interested in getting tested for them.

First, it’s important to understand the differences between allergies, sensitivities, and intolerances. If you’re not sure which one (or ones) you are suffering from, read this article.

If it sounds like allergies are your thing, here’s some more information to help you understand which type of testing might be best for you.

What types of tests are there?

Food allergies are diagnosed through skin prick tests or IgE allergy blood tests.

Skin Prick Tests:

Quick Facts:

  • Also sometimes called a scratch test.
  • Typically quick and inexpensive, performed during an office visit.
  • Cannot be on anti-histamines during testing because they will blunt the responses.

How does it work?

Your physician will place liquid solutions on your skin that contain various food antigens, then use a small needle to lightly poke those areas, allowing some of the liquid to seep under the skin and come in contact with your mast cells. (Not sure what mast cells are? Read this article.)

If you are allergic to the food or substance tested, you will develop a wheal in that area (a white bump with a red inflamed ring around it, like a mosquito bite). Generally, the larger the wheal the more likely it is that you are allergic to that substance, and if there is no wheal, you are probably not allergic.

These tests don’t really hurt & results are seen within 30 minutes.

Is it accurate?

Skin prick tests have a roughly 50% false-positive rate (when the test says you are allergic to a substance when you really aren’t), so it is necessary to take the results with a grain of salt.

These false positive occur because when the antigens are pushed under the skin, they are directly exposed to the IgE molecules in their whole form. In contrast, when you eat a food, your digestive system may break down some or all of the food antigens, changing their structure and decreasing their size to the point where your IgE molecules no longer recognize them as a threat. So while your body may react to the full form of the antigen being pricked under the skin, it may NOT react to the same protein after it has been digested & absorbed into the bloodstream when you eat the food.

False positives can also occur when the IgE molecules flag foods in the same “food family” as a food you are actually allergic to. For example, mango & cashews are in the same food family (evergreen tree family). You may only actually be allergic to cashews, but the IgE molecules may pick on the similar structure of the mango protein, and cause mast cell degranulation, even though in real life, when you eat and digest the food, it doesn’t cause a reaction.

Skin-prick tests are more useful for environmental inhalant allergens like pollen or pet dander than they are for food allergens. Additionally, extracts are not available for all food allergens.

Serum Specific IgE Allergy Blood Tests:

The second way to get tested for food allergies is through blood testing. There are different types of blood tests, so speak with your allergist to find the best one for you.

One of the newer tests, ImmunoCAP, offered by Quest Diagnostics, is an improvement upon the former ELISA & RAST techniques, and is most commonly used. ImmunoCAP uses cellulose binding discs, which have better binding capacities for the allergens than the paper & plastic discs used in ELISA & RAST. This means it has fewer false negatives (when the test says you’re not allergic but you actually are).

Perks of doing a blood test:

  • You CAN be on anti-histamines when you get tested, which makes it great for people with severe allergies or skin rashes over large areas of their bodies.
  • Since the blood is tested outside of the body, there is no risk of anaphylaxis.

How does it work?

The test is ordered by your physician or allergist, and the blood is drawn at a local lab. The blood is then shipped to a lab for processing, and the results are sent to your doctor for interpretation.

Once the results are in, you can schedule an appointment with your doctor to go over them.

Is it accurate?

While the blood test can tell you whether you have IgE antibodies to specific substances, it can’t tell you about the severity of your reaction, since the amount of antibody is not directly related to severity of symptoms. In other words, it can tell you whether your body is sensitized to certain foods, but not whether eating them will trigger a full blown allergic reaction. This could mean unnecessary dietary restriction when it is not actually needed.

To help interpret the results with more accuracy, your doctor will likely ask you for a food diary to draw connections between foods consumed & symptoms experienced. This helps avoid unnecessary dietary restriction for foods that do not actually cause symptoms.

Blood tests are slightly more accurate than skin prick test for food allergens (40% false positive rate compared to 60% on skin prick), but are still less than perfect.

For this reason, sometimes the two tests are used together to gather as much information as possible.

Other Methods:

You can also try to deduce which foods you are allergic to without skin-prick or blood testing, under the guidance of a trained physician.

1) Oral Tolerance Test

If the physician feels it is medically appropriate, they may do an oral tolerance challenge with you, in which they feed you increasing amounts of the suspected allergen under medical supervision and watch your reaction. It is CRITICAL to only do this under the direct care of a physician with an epi-pen on hand to counteract any allergic reactions.

2) Elimination Diets

Your doctor may also recommend an elimination diet, in which you stop eating the “Big 8” allergens (milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, and soy) and see if your symptoms improve.

If they do, then you can assume at least 1 of those allergens was triggering your symptoms. Once the symptoms are gone, you reintroduce each allergen one at a time and watch for any reactions. If you have a reaction after reintroducing one of the Big 8 allergens, you know that you are allergic to that food & should stop consuming it. Chances are you aren’t allergic to ALL of the Big 8, so after reintroduction you will probably be able to consume some of those foods again.

While the Big 8 cover 90% of the most common food allergens, there’s still a chance that you are allergic to something else not included on this list, like, avocado, for example. This is where testing can help narrow down the picture.

Looking for an allergist?

You can ask for a referral from your physician or use the “Find an Allergist” search tool from The American Academy of Allergy, Asthma, and Immunology.

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The Physiology of Food Allergies

Photo Oct 26, 8 44 31 AM

Food allergies are relatively common in the United States.

According to research estimates, they affect:

  • 8% of children
  • 5% of adults (because some kids grow out of their allergies)

The “Big 8” most common food allergens include:

  • Peanuts
  • Tree nuts
  • Fish
  • Shellfish
  • Cow’s milk
  • Egg
  • Soy
  • Wheat
[PS- If you’re not sure what the differences are between an allergy, sensitivity, and intolerance, check out this article.}

The first step in becoming allergic to a food is “losing oral tolerance”.

This is a fancy way of saying that your body is losing the normal (tolerant) response to the food, and going rogue.

To develop a full-blown allergic response to a food, it actually requires TWO exposures to the food.


On the first exposure, your body has to decide whether this new food is friend or foe. For some reason (probably largely genetic), some people have over-protective immune systems that tend to flag ordinary foods as threats.

Once the immune system has flagged the food as a threat, it starts preparing to defend itself for the next exposure.

To do this, your body’s B-cells (the type of immune cells that make antibodies) start producing antibodies against the threatening food. The type of antibody involved in allergies is called IgE (immunoglobin E) (immunoglobin is just another name for antibody).

Here’s what an IgE antibody looks like:

Screen Shot 2016-10-26 at 10.55.38 AM

Each “threatening” food gets its own unique type of antibody that is only capable of binding to that specific food antigen.

So, on the first exposure, you don’t actually feel any symptoms. Although your body knows it doesn’t like that food, it’s not ready to immediately launch an attack (that takes some time and energy, after all).

In-between the first & second exposure, your body is preparing itself for a second attack.

Once your body has made a whole bunch of IgE for the offending food, those antibodies circulate around your blood stream & attach themselves to mast cells.

Mast cells are a type of tissue-specific white blood cell, located on membranes of your body, like the skin, mucous membranes, GI tract, and lungs.

Mast cells contain packets (called granules) of pain-causing & inflammation-inducing chemicals that they store up & are ready to release into the environment at a moment’s notice. These chemicals (also known as “mediators”) are responsible for creating the unpleasant symptoms of an allergic response.

Here’s what mast cells look like when they have IgE antibodies attached to them:


The IgE antibodies are kind of like soldiers, guarding your body from any threats, always on the lookout for the presence of the “threatening” food. Fun fact: one mast cell can have 100,000 different IgE molecules on its surface!

The second time you eat the offending food, your body’s immune system is ready and waiting with IgE “soldiers” mounted on mast cells. This time, you WILL have an allergic reaction.

Here’s what happens:

You eat the offending food, digest and absorb it into your bloodstream. Now those food antigens are circulating through your blood. Eventually, the food antigens will come into contact with the IgE antibodies mounted on your tissue’s mast cells.

When this happens, the IgE antibodies latch onto the food antigen and “capture” it (this is called crosslinking, because it happens when two IgE antibodies attach to the same food antigen). It’s sort of like when two soldiers capture an enemy who is trying to infiltrate their castle. “Aha!”, they say. “We’ve got you now! Time for punishment.”

The attachment of the food antigen to the IgE antibodies causes the mast cell to “degranulate”, aka release packets (granules) of pro-inflammatory molecules like histamine and cytokines, which trigger an allergic reaction.


The purpose of degranulation is to destroy the threat.

The chemical mediators (like histamine) released from the mast cell cause physiological changes in your body. In fact, they are called “mediators” because they do just that. They “mediate” changes in the body.

Each mediator causes a unique physiologic change, but in general, they increase blood flow to the area and increase blood vessel permeability so that more immune cells can come to the area and attack the threat (this is also what causes redness and swelling). The mediators also increase smooth muscle contraction to help expel any allergens from the lungs or GI tract (and cause symptoms of asthma and diarrhea).

The symptoms you experience depend on which mast cells degranulate.

For example, if the mast cells in your skin degranulate, you may get hives. If the mast cells in your lungs degranulate, you may have trouble breathing or develop an asthma attack. If the mast cells in your GI tract degranulate, you may get diarrhea.

If mast cells start degranulating all over your body, you are experiencing anaphylaxis, a serious and potentially life-threatening reaction that may require an epinephrine injection to combat.

When anaphylaxis occurs, many mast cells degranulate at once, causing blood vessels all over the body to increase their permeability. This causes too much liquid to leak out into the tissues, leading to severe swelling and a dangerous drop in blood pressure that can cause your organs to stop functioning. A quick shot of epinephrine (adrenaline) is need to rapidly constrict blood vessels & bring blood pressure back up to normal.

Symptoms of a food allergy usually occur rapidly, about 5-30 minutes after ingestion of the offending food, and are typically obvious to the person they are affecting.

So, in summary, the steps of an allergic response are:

Step 1: Sensitization

  • Your immune system flags a food you’ve eaten a threat
  • B-cells produce large amount of IgE antibodies for that food
  • These IgE antibodies dock themselves on mast cells located in your tissues, and wait for the next exposure to that food
  • You don’t experience any symptoms at this time

Step 2: Allergic Response

  • You eat the offending food again
  • The food antigens crosslink to the waiting IgE antibodies on the mast cells
  • The mast cells “degranulate” and release pro-inflammatory & pro-algesic (pain causing) chemical mediators into the surrounding tissue
  • This causes the symptoms of an allergic response, like swelling, itching, trouble breathing, etc.
  • The symptoms will subside when exposure to the allergen is gone, or when anti-allergy medications, like anti-histamines, are taken.

Stay tuned for more articles on allergies, sensitivities, and intolerances. If you’d like a broad overview of how these 3 conditions differ, check out this article.

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What is the difference between a food allergy, sensitivity, and intolerance?

allergy sensitivity intolerance

It’s common knowledge that people can react negatively to food.

  • Sometimes people start wheezing or break out into hives.
  • Sometimes they have an uncomfortable increase in gas and bloating.
  • Sometimes they get congestion or swelling.
  • Sometimes they get diarrhea, constipation, or even mucus in stools.
  • Sometimes they get migraines.

With so many possible symptoms, how do you know whether you have an allergy, a sensitivity, or an intolerance to food?

It’s true, all three types of reactions can produce similar symptoms, but via very different biological pathways.

In a nutshell, here are the differences:

  1. A food allergy involves IgE antibodies, and typically produces a reaction within 30 minutes of eating.
  2. A food sensitivity still involves the immune system, but NOT IgE antibodies, and the reactions are typically more delayed (up to 72 hours after eating).
  3. A food intolerance does not involve the immune system at all, and is caused by a lack of appropriate enzymes to digest certain foods.

Food allergies are most common with the “Big 8”:

  1. Peanuts
  2. Tree Nuts
  3. Cow’s Milk
  4. Egg
  5. Fish
  6. Shellfish
  7. Soy
  8. Wheat

90% of the time, food-related allergic reactions are caused by one of these foods.

Most people will know right away if they have a food allergy, since they will develop quick symptoms like hives, diarrhea, or trouble breathing. True food allergies are Type I hypersensitivity reactions, involving IgE antibodies and the degranulation of mast cells in connective tissue, like the lungs, skin, and lining of the GI tract.

Food allergies can be diagnosed using a skin-prick test, an IgE blood test, an elimination diet, or in some cases, an oral tolerance challenge.

The best way to handle allergies is to work with an allergy specialist. Typically your food allergens must be avoided indefinitely to avoid symptoms.

In contrast… food sensitivities are more likely to occur with ANY food or chemical.

Yep, even “healthy” foods like lettuce, salmon, or even turmeric! It’s also totally possible to be sensitive to chemicals that are added to our foods, like food colorings, caffeine, solanine (in nightshade vegetables), or artificial sweeteners.

Unlike allergies, food sensitivity reactions are often delayed, occurring up to 72 hours after ingestion. They are also triggered by multiple pathways of the immune system (Type III and Type IV hypersensitivity reactions), and DON’T involve IgE antibodies or mast cells.

Instead, they can involve immune complexes with other types of antibodies (IgG or IgM), or no antibodies at all, instead involving antigen presenting cells and T-cells. (For more details the physiology of food sensitivities, read this article.)

Since food sensitivities are not mediated by IgE antibodies & mast cells, traditional allergy testing does NOT test for them.

The most accurate method for food sensitivity testing is MRT, which stands for Mediator Release Test. It’s a blood test that measures the magnitude of your body’s inflammatory response to foods, via either the Type III or Type IV hypersensitivity pathways.

MRT is great because it doesn’t matter exactly which pathway is causing your symptoms (IgG, IgM, T-cells, etc.). MRT tests the amount of pro-inflammatory mediators released, no matter which pathway triggered them, so you can know for sure which foods are likely contributing to (or not contributing to) your food sensitivity symptoms.

The best way to be tested for food sensitivities is through a Certified LEAP Therapist (CLT). CLTs are certified in food sensitivities, the MRT test, and the implementation of the corresponding therapeutic diet, known as LEAP (Lifestyle Eating and Performance). You can find a CLT near you by searching on healthprofs, or, depending on your state’s licensure laws, you may be able to work remotely with a CLT (like me!) via telephone or Skype.

Food sensitivities are often a symptom of a deeper root cause, such as gut dysbiosis, infections/parasites, or low stomach acid. They can also be influenced by genetics or triggered by stressful events such as childbirth or serious illness.

However, food sensitivities are typically not permanent, and once the body system is healed, food sensitivities tend to decrease. Many people can eventually resume eating some of the foods they were once sensitive to, even if only in small doses.

Finally, food intolerances do not involve the immune system at all.

Food intolerances are far and away more common than food allergies or sensitivities. In fact, up to 75% of the world’s population is lactose intolerant!

Food intolerances occur when the body lacks the correct enzyme to break down a food product.

Lactose intolerance is the most common type of food intolerance, and is caused by the body’s natural decrease in the production of the enzyme lactase, which breaks down the milk sugar called lactose.

Without enough of the enzyme lactase, the lactose sugar remains undigested, and passes into the large intestine in its whole form. This increases the osmotic load of the stool, and causes water to rush into the colon. Of course, this then leads to uncomfortable diarrhea. When lactose sugar enters the colon, it is also rapidly fermented by your gut bacteria, producing the tell-tale gas and bloating.

It is also possible to be intolerant to other sugars, such as fructose, but this is much less common. Other types of intolerances include histamine intolerance (when the body cannot properly breakdown histamine in food, causing allergy-like symptoms), and amine intolerance (in aged foods).

While food intolerances are very uncomfortable, they can be treated by avoiding the food you are having trouble digesting, taking appropriate digestive enzymes with meals, or by consuming products that contain pre-digested forms of the intolerant molecule (like Lactaid milk, which contains pre-digested lactose).

If you are having uncomfortable symptoms after consuming foods, I highly recommend working with a Certified LEAP Therapist or other Registered Dietitian who is well-versed in allergies, sensitivities, and intolerances.

If you would like to book a session with me, shoot me an email at erica@ericajulson.com.

All sessions are held virtually, via telephone or skype. I look forward to “meeting” you!

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