See an allergist. If you don’t already have an allergist, go to your family doctor and ask to be referred to one; a good allergist is like a private investigator who can usually single out the culprit in no time. When it comes to food allergies, an accurate diagnosis is key, or else you risk giving the boot to foods that are just fine, and keeping the trouble-makers around.

Keep a journal. As soon as you suspect a food allergy, keep a careful journal of everything you eat, your activities, and any symptoms you experience. You may suspect that a particular food is causing your reactions, but it could be a different offender altogether – and your journal will help you and your allergist arrive at an accurate diagnosis. (Allergists consider the “reaction history” a key part of the process.)

Take the test. When you see your allergist, he or she will likely want to perform one or more tests to pinpoint your allergy. The following are the types of tests available.

1. The Skin-Prick Test

This is by far the most common allergy test, and is usually performed in the allergist’s office. A drop of a serum that contains the allergen is placed onto the patient’s forearm or back, and is then pricked with a small needle so the allergen goes slightly under the skin’s surface. (This is not at all the same sensation as getting an injection or blood test; it’s more like a small pin prick.)

If you are sensitized to an allergen and it is put under the skin, antibodies attack and create a small red bump called a hive – so if a hive forms where the serum was placed, it indicates a possible allergy.

It is important to note, however, that if a hive does form, it does not necessarily mean you will react when you eat the food. In fact, some studies have shown that only half of the people who have positive skin tests are actually allergic to the food, so a positive test is only one indicator of a possible allergy.

But the bigger the hive that forms, the more likely it is the person will react when he or she eats the food. (False negatives are also possible, but are uncommon.)

Need to Know

• It is important that you avoid taking antihistamines for at least 48 hours before the prick test, or the results may be inaccurate.

• Serious systemic reactions to the skin-prick test are possible – but extremely unusual. So skin-prick tests are considered a simple and safe tool in allergy diagnosis.

The skin-prick test replaced the traditional “scratch test”, in which a drop of serum was put on the skin and then scratched with a pin, because the scratch test put more allergen under the skin and came with a greater risk of a serious reaction.

2. Specific IgE Blood Test (RAST, UniCAP, ImmunoCAP)

Blood tests are a less common method of diagnosing allergy, because they are much more expensive and not necessarily more accurate – but they are sometimes used when a patient has a skin condition that makes prick testing difficult, when a serious allergy is suspected.

They are also often used to help confirm the results of a prick test.

For this test, a blood sample is taken then sent to a laboratory for testing. At the lab, the blood is put in contact with an allergen in a dish; if the patient is sensitized to that allergen, the antibodies in the blood will attach themselves to it.

A substance that recognizes those allergen-attached (IgE) antibodies is added, and then they are counted. The higher the number of those allergen-attached antibodies, the greater the likelihood the patient will react when exposed to that substance.

The downsides of the test are that they are considered less accurate, and they lead to more false negatives. In fact, if the test is negative, the patient still has a 15-20 per cent chance of being allergic to that substance.

Like the skin-prick tests, a positive test does not necessarily mean you’ll react when you eat the food. However, if a test comes back with a very high number of allergen-attached antibodies, there’s a greater likelihood a reaction will occur when the food is eaten.

3. Intradermal Test

An intradermal test is similar to a skin-prick test in that a small amount of an allergen is introduced to the skin, and if a hive forms, the test is considered positive. The main differences are that the serum is more diluted, and it is put more deeply under the skin’s surface, where it is more likely to react.

Intradermal tests aren’t used as often as they once were, because they can result in more serious reactions, and are usually only administered after a prick test has come back negative. They are most commonly used to test insect venoms and drugs, starting at very low concentrations, then working up slowly. They are rarely used for food testing.

This type of test is more sensitive, so can give clearer results – but they also tend to lead to more false positives. On the upside, there are fewer false negatives.

Anaphylaxis Note: It’s important to note that none of these tests (prick, intradermal, blood) can predict whether or not a person will go into anaphylaxis, the most serious form of allergic reaction. Some people assume that the more severe the reaction on the skin or in the blood, the greater the chance of anaphylaxis – but this is not statistically true.

These antibodies attach themselves to mast cells in the body, and when the person again eats the allergenic food, the proteins from it become attached to the IgE antibodies.

This causes the mast cells to degranulate, releasing histamine and other powerful chemicals. It is these chemicals that cause the symptoms of allergy.
See: The Signs and Symptoms

What is Anaphylaxis?

There is a name for the severe form of allergic reaction: anaphylaxis. This is an emergency medical event involving one or more of the body’s systems: respiratory, gastrointestinal (the gut), the skin and the cardiovascular system (e.g. a drop in blood pressure).

In an anaphylactic reaction, a person can lose consciousness with a drop in blood pressure. Anaphylaxis can be fatal, which is why food-allergic individuals and parents of kids with food allergies are instructed by allergists to avoid even trace amounts of specific allergens: e.g. peanut, nuts or mlk.

Allergic reactions are notoriously inconsistent. An individual might have a minor reaction on one exposure to a food (e.g. a cashew) but another time have anaphylaxis.

The risk of severe reaction is higher in those with asthma, and those who have had a previous serious reaction. That said, there are instances of anaphylaxis without asthma or previous serious reaction. So if a person is food allergic, there is always a risk of anaphylaxis. So far, there is no way of measuring this level of risk, but researchers are beginning to locate markers that may lead to a test down the road.

Top 8 Food Allergy Triggers (United States)
These “priority allergens” cause the majority of food allergy reactions:
• peanuts
• tree nuts (e.g. almonds, cashews, hazelnuts, pecans, walnuts)
• milk
• egg
• shellfish (shrimp, crab, lobster, mussels, clams)
• fish
• soy
• wheat

Top 11 Food Allergy Triggers (Canada)
These “priority allergens” cause the majority of food allergy reactions:
• peanuts
• tree nuts (e.g. almonds, cashews, hazelnuts, pecans, walnuts)
• milk
• egg
• shellfish (shrimp, crab, lobster, mussels, clams)
• fish
• soy
• wheat
• sesame
• mustard
• sulphites (Health Canada also lists these food additives as one of the common causes of reaction, though it is not a food protein.)

A Note on Food Intolerance: This sensitivity can cause gastrointestinal distress, but it does not involve the immune system or a reaction to the proteins in food. An intolerance is not an allergy.

Perhaps you have experienced unexplained skin rashes (known as hives) or vomiting or diarrhea? Does your child refuse to eat a certain food, or complain that it makes his “tongue hurt”? These could be signs of a food allergy, and should be taken seriously.

It is common for the symptoms of food allergy to vary by individual – and from reaction to reaction in the same person. Not everyone will get all the symptoms, which range greatly in severity from mild to severe (and even fatal): your throat may feel tight on one exposure to your allergen or you may get itchy hives on your skin and vomiting with the next.

The Range of Symptoms

-Tingling in the mouth
-Swelling of the tongue and throat / feeling of throat tightness
-Itchy skin, hives or skin redness
-Abdominal cramps
-Vomiting or diarrhea
-Breathing difficulty, wheezing
-Faintness due to a sudden drop in blood pressure

Symptoms reviewed by Dr. Susan Waserman

Anaphylaxis

Anaphylaxis is the severe form of allergic reaction. It involves one or more of the body’s symptoms; for example, the gastrointestinal tract, the respiratory tract, the skin and the cardiovascular system. A person experiencing anaphylaxis often has difficulty breathing, and the person could lose consciousness. Anaphylaxis puts a person at risk of death.

Anaphylactic reactions can come on quickly, and it’s impossible to know when a reaction will become severe. It’s important that people with food allergies are prepared for a reaction by always carrying an epinephrine auto-injector (either EpiPen or Auvi-Q/Allerject).

Experts recommend using epinephrine early if a person known to be at risk of anaphylaxis begins to show signs of allergy symptoms – don’t wait until the symptoms worsen, as it may become to difficult put a halt to the reaction once it’s in progress.