CENTER ON BEHAVIORAL MEDICINE

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Testing  for Food Allergies
Permission graciously given by the author to reproduce this paper: 

This material taken from:  James Braly, M.D.
www.drbralyallergyrelief.com/ www.betterhealth.vic.gov.au
 

ALLERGY TESTING

 A wide variety of allergic conditions exist. Allergy testing is the procedure used to determine which particular substances (allergens) are responsible for provoking an allergic reaction. The procedure used depends on the type of allergy. Common symptoms of food allergies include itching and burning around the mouth, asthma and vomiting. About 90 per cent of food allergies are caused by nuts, egg, milk or soy. Asthma and hay fever are allergic reactions to substances in the environment, and different people are sensitive to different types of allergens. Common asthma allergens include cigarette smoke and dust mites, while pollen and grasses commonly trigger hay fever in susceptible people.  Allergies that can lead to sever reactions within a few minutes are called Type 1 or immediate-onset allergies.  They involve the IgE immunoglobulin.  A second type of allergy is the Type 3 or delayed-onset allergies which are also called food intolerances and involve the IgG immunoglobulin.  A more detailed discussion on Type 1 and Type 3 food reactions can be found at the end of this paper.

Problems associated with allergies

Some of the problems associated with allergies include: 

•    Skin rashes 
•    Running nose and teary eyes 
•    Sneezing 
•    Asthma attacks 
•    Nausea and vomiting 
•    Abdominal cramps 
•    Fatal anaphylaxis (the breathing tubes in the lungs tighten to such an extent
     that respiration is impossible).

The procedures

Many medical tests can determine the presence of an allergy. More specific tests are required to determine exactly which substance or substances are causing the allergy. These tests include: 

•    Prick tests - also known as scratch tests. This type of test is often used for allergic asthma. Various reagents are applied to the forearm with a dropper, and the skin gently pricked or scratched with a needle. A 'reagent' is a solution that contains common allergenic substances including some foods, yeast, animal hair, dust mites etc. A positive result shows within 20 minutes as a red weal or flare. False reactions are common. 

•    Patch tests - most commonly used to investigate contact dermatitis. Common allergens include fragrance, nickel (in jewellery, watch buckles and coins) and chrome (in leathers and bricklayers' cement). The reagents are available as patches arranged along adhesive strips. The strips are applied to the back, and the area is examined after 48 and 96 hours. A positive result shows as redness or blisters at the site of a particular reagent. 

•    Radio allergosorbent test (RAST) - a more accurate form of allergy testing, done when skin testing is impossible or skin tests are inconclusive. Blood is taken and the suspected allergen is mixed with the blood. The level of IgE (an immunoglobulin associated with allergic reaction) produced is measured.  The RAST tends to give false negatives, that is, indicate that a person is not allergic when in fact he is.

•    Enzyme-linked Immunosorbent Assay (ELISA) combine the specificity of antibodies with the sensitivity of simple enzyme assays, by using antibodies (what the body produces) or antigens (the offending agent) coupled to an easily-assayed enzyme. ELISAs can provide a useful measurement of antigen or antibody concentration. There are two main variations on this method: The ELISA can be used to detect the presence of antigens that are recognized by an antibody or it can be used to test for antibodies that recognize an antigen. This test is used to identify the presence of the IgG family.  (There are four sub-classes of IgG (IgG1, IgG2, IgG3, IgG4) and clinical research has identified that significant allergens are mediated by all four. ) It tends to give false positives, that is, the test indicated that a person is allergic when in fact she is not.

•    Elimination diets and challenge testing - an elimination diet is used to isolate foods which are allergenic. It usually takes place over a number of weeks, and involves strict avoidance of a number of foods that have been identified as common causes of food allergy. These include milk, eggs, soy products, wheat, shellfish, peanuts, yeast and chocolate. No foods or fluids may be consumed other than those specified in the starting diet. If symptoms improve, foods are added one at a time until symptoms occur. Usually, a diary is kept to record any symptoms so they can be linked to the correct food.

•    After the test
If undergoing a skin prick test, your doctor will examine you for signs of an allergic reaction after 20 minutes or so. Patch tests require subsequent visits 48 and 96 hours after application. The results of blood tests may take a week or so, while an elimination and challenge diet may take many weeks to provide results. Be guided by your health care professional. If the results to your tests are negative, you are not allergic to that particular substance. A positive result means you are allergic to that substance, and you must take care to avoid it in future. 

Possible complications

Some people with allergies experience severe reactions when exposed to particular allergens. For example, the red weals associated with skin prick tests can be painful, inflamed and irritated. Some reactions, such as anaphylactic shock, are potentially life threatening. It is important that allergy tests be performed by a qualified health professional, who can anticipate and treat any allergic reactions you may have.

Long term outlook

Allergy testing can help a person suffering from allergies to determine which particular allergens are triggering their symptoms. In many cases, an experienced allergist can offer immunotherapy to gradually increase the patient's tolerance, to the point where symptoms are no longer experienced on exposure to the allergen or, at least, are experienced to a lesser degree.

Other forms of treatment for allergies include:

•    Avoidance of the allergens. 
•    Barrier methods, such as using air filters in your home. 
•    Medications to treat the symptoms, including over-the-counter medications
     available from your chemist (such as antihistamines and decongestants). 
•    Steroids and other drugs prescribed by your doctor that may be helpful to manage
     symptoms.

Contrary to popular belief, food allergies (Type 1 Immediate-onset Allergies) are rare. Most reactions to food are a food intolerance (Type 3 Delayed-onset Allergies). The symptoms usually affect three main sites of the body - the skin and the respiratory and digestive systems.

Allergy

Type 1 reactions are an over-reaction of the body's immune system to a specific component, usually a protein. These proteins may be from foods, pollens, house dust, animal hair or moulds and are known as allergens. The word 'allergy' means that the immune system has responded to a harmless substance as if it were toxic. 

Food intolerance

Type 3 reactions (also referred to as a food intolerance) unlike food allergies (Type 1 reactions) which can be life threatening, are a reaction that some people have after eating or drinking.  Food intolerance has been associated with asthma, Chronic Fatigue Syndrome and Irritable Bowel Syndrome (IBS). 

Food intolerance is much more common than food allergy. 

Symptoms of allergy and intolerance

The symptoms to a food allergy or intolerance are often difficult to distinguish. As the symptoms can also be caused by other conditions, medical diagnosis is always needed. 

Symptoms of food allergy

The onset of symptoms from food allergy tend to be more immediate and can be life-threatening. Common symptoms include: 
•    Itching and burning and swelling around the mouth 
•    Runny nose 
•    Skin rash and hives, eczema, urticaria (skin becomes red and raised) 
•    Diarrhoea, abdominal cramps 
•    Breathing difficulties, including wheezing and asthma 
•    Vomiting, nausea 
•    Life-threatening anaphylaxis.

Symptoms of food intolerance 

Symptoms of food intolerance may be immediate but are often delayed and are triggered only after a threshold level of exposure is reached. They can include: 
•    Nervousness, tremor 
•    Sweating 
•    Palpitations 
•    Rapid breathing 
•    Headache, migraine 
•    Diarrhoea 
•    Burning sensations on the skin 
•    Tightness across the face and chest 
•    Allergy-like reactions due to histamine and other amines in some foods 
•    Asthma from food containing benzoates, salicylates, MSG and sulphite
     derivatives.

Allergy on the increase

Allergies are on the increase worldwide and in recent food allergies have become more prevalent, particularly peanut allergy in preschool children. In June 2002, 6.2 per cent of preschool children in NSW had a food allergy, with the reported prevalence of peanut and nut allergy at less than 2 per cent. About 60 per cent of allergies appear during the first year of life, with cow's milk allergy being one of the most common in early childhood. Most children grow out of it before they start school. Less than one per cent of adults have food allergy, usually to peanuts, nuts and fish. 

Affected body parts

Various sites on the body can be targeted by a reaction to food, including: 
•    Eyes - itching, watering 
•    Nose - stuffiness, sneezing 
•    Mouth - itching, swelling 
•    Throat - swelling 
•    Digestive system - stomach pains, vomiting, diarrhoea 
•    Skin - rashes, such as hives (urticaria) or atopic dermatitis 
•    Lungs - asthma, more common in children than adults 
•    Central nervous system - headache, irritability, fatigue, convulsions.

Anaphylactic shock is life threatening

Anaphylaxis, or anaphylactic shock, is an allergic reaction that needs urgent medical attention. Eggs, milk, peanuts, sesame, shellfish, berries and soy are common anaphylactic allergens, so are some medications and insect bites. Within minutes of exposure to the allergen, the person's airways can swell to the point of suffocation. To prevent severe injury or death, the person often needs an injection of adrenalin, which can be intramuscular. Home kits of professionally prepared adrenalin needles are available from chemists. 

The symptoms of anaphylactic shock include: 
•    Itchy palms and soles, hives 
•    Tingling and warmth 
•    Asthma, wheezing and breathing difficulties 
•    Swelling of the face 
•    Choking 
•    Fainting 
•    Drop in blood pressure. 

Food allergy can be inherited

Children who have one family member with asthma or eczema have a 20-40 per cent higher risk of developing allergy; if there are two or more family members with allergies then the risk increases to 50-80 per cent. 

Preventing food allergy

Allergy prevention in children is an active area of research. Findings to date indicate that: 
•    Prenatal - there is no conclusive evidence that allergen avoidance in pregnancy is beneficial. Exposure to allergens in gestation may help promote immune tolerance. 
•    Postnatal - exclusive breastfeeding during the first 4-6 months appears to protect against the development of allergy and helps to enhance immune activity. Exposure to cigarette smoke, house dust, mould and animal hair and early introduction of solids can increase the risk of developing allergies. 

Food allergy - the common culprits

About 90 per cent of allergies are caused by nuts, eggs, milk or soy. Peanut allergy is one of the most common allergies in older children. Other foods that cause allergies include (in order from the most common): 
•    Egg 
•    Peanut 
•    Milk 
•    Other nuts 
•    Sesame 
•    Fish 
•    Grains such as rye, wheat, oats 
•    Soy 
•    Molluscs, such as oysters, mussels, clam, squid and octopus 
•    Crustaceans, such as lobster, prawn, crab, shrimp 
•    Fruit, berries, tomato, cucumber, white potato or mustard.

Food intolerance - the common culprits

The foods that tend to cause intolerance reactions in sensitive people include: 
•    Dairy products, including milk, cheese and yoghurt 
•    Chocolate 
•    Egg, particularly egg white 
•    Flavour enhancers such as MSG (monosodium glutamate) 
•    Food additives 
•    Strawberries, citrus fruits and tomatoes 
•    Wine, particularly red wine.
Reactions may not always occur, as they are usually related to the amount of food consumed. A small amount may not cause any reaction.

Tracking down the allergen

In most cases, symptoms appear within a few minutes of eating the particular food, which makes pinpointing the allergen an easy task. However, if the cause is unknown, diagnostic tests may be needed such as: 
•    Keeping a food and symptoms diary to check for patterns. 
•    Cutting out all suspect foods for two weeks, then reintroducing them one at a time
      to test for reactions (except in cases of anaphylaxis). 
•    Skin prick tests using food extracts. 
•    Blood tests.

Avoiding the food

The easiest way to treat a food allergy or intolerance is to eliminate it from the diet. Sometimes, the body can tolerate the food if it is avoided for a time, then reintroduced in small doses. Before you eliminate foods from your diet, seek advice from a doctor or dietitian. 

Food laws and labels

Food laws require food labeling to declare certain substances in foods and certain foods including: 
•    Cereals containing gluten and their products 
•    Crustacea and their products 
•    Egg and egg products 
•    Fish and fish products 
•    Milk and milk products 
•    Nuts and sesame seeds and their products 
•    Peanuts and soybeans, and their products 
•    Added sulphites in concentrations of 10mg/kg or more 
•    Royal Jelly presented as food or present in food, bee pollen and Propolis.

These foods must be declared whenever they are used as an ingredient or part of a compound ingredient (even if they are carry-over ingredients); a food additive or compound of a food additive; a processing aid or component of a processing aid.

To avoid allergic foods, learn the terms used to describe these foods on foods labels, for example: 
•    Milk protein - milk, non-fat milk solids, cheese, yoghurt, caseinates, whey, lactose. 
•    Lactose - milk, lactose. 
•    Egg - eggs, egg albumen, egg yolk, egg lecithin 
•    Gluten - wheat, barley, rye, triticale, wheat bran, malt, oats, cornflour, oatbran. 
•    Soy -soybeans, hydrolysed vegetable protein, soy protein isolate, soy lecithin. 
•    Salicylates - strawberries and tomatoes.

Food Allergy and the Immune System

A food allergy develops when the immune system, by means of an odd mixture of immune cells, antibodies and chemical mediators, reacts in an attempt to reject a food  in your diet. 

There are four different types of immune reactions in food allergy. These are called Types 1, 2, 3, and 4.  More than one type of reaction can occur at the same time in the same allergic individual. Types 1 and 3 will be our focus of this section. 

Type 1 Immediate-Onset Food Allergies

The best known and well-studied form of food allergies is called a Type 1 immune reaction. Type 1 food allergies occur in less than 5 percent of the population -- mostly in children,  They are also called immediate-onset, IgE-mediated and/or atopic food allergies. Usually occurring in the genetically predisposed individual, the immune system begins creating a specific type of antibody called IgE (immunoglobulin IgE) to certain foods. One side of the IgE antibody will recognize and tenaciously bind to the allergic food. The other side of the antibody is attached to a specialized immune cell packed with histamine, called the Mast cell. Primed for action, the IgE antibody now only have to patiently wait for re-exposure to food allergens. 

When you eat the allergic food the next time,  IgE antibodies hungrily latch onto the food.  Instantaneously histamine and other allergy-related chemicals -- called chemical mediators  -- are released from the mast cell,  rapidly bringing on the unwelcome appearance of  stomach cramping, diarrhea, skin rashes, hives, swelling, wheezing or the most dreaded  of  Type 1 reactions, anaphylaxis. 

Type 3 Delayed-Onset Food Allergy/Intolerance

Type 3 immune reactions are much more commonly involved in food allergy than Type 1 reactions.  A Type 3 food allergy, often referred to as food intolerances to distinguish it from the Type 1 reactions, also involves the immune system.  They occur when your immune system creates an overabundance of IgG antibodies to a particular food.  The IgG antibodies, instead of attaching to mast cells like IgE antibodies in Type 1 allergies, bind directly to the food as it enters the bloodstream, forming different sizes of so-called circulating immune complexes (food allergens bound to antibodies circulating in the bloodstream).  The allergic symptoms in Type 3 immune reactions are delayed in onset, appearing anywhere from within two hours up to several days after consuming allergic foods (Example: migraine headaches characteristically first appear 48 hours after allergic foods are eaten).  Delayed food reactions may emanate from any organ or tissue in the human body, provoking over 100 allergic symptoms and well over 150 different medical diseases.  An estimated 60 to 80 million Americans suffer from clinically significant food allergies, most all of whom suffer delayed symptoms. 

Immediate vs Delayed Food Allergy

Here's a overview of the important differences between these two types of food allergies: 

Once thought to be the only "true" food allergy, immediate food allergy is common in children, but rare in adults. 
Once thought to be uncommon at best, delayed food allergy is now thought by many investigators to be quite common.  In fact, it is the most common form of food allergy in children and adults. 

Allergic symptoms in immediate reactions occur within two hours of  eating. Allergic symptoms in delayed reactions 
do not appear for at least 2 hours, not infrequently showing up 24 to 48 hours later (there are even reports of delayed 
symptoms appearing 3 to 7 days after eating). 

Immediate-onset food allergy involves one or two foods in the diet, as a rule. Delayed reactions characteristically 
involve 3 to 10 foods, sometimes as many of 20 foods in very allergic, "leaky" individuals. 

Because a small amount of a single food is involved and the allergic symptoms appear immediately, immediate 
food allergy is usually self-diagnosed. You eat the food. It causes symptoms quickly. You see the connection. You stop 
eating it.  Due to a combination of delayed symptoms, multiple foods, and food cravings, Type 3 delayed-onset food 
allergies are rarely self-diagnosed. To detect the allergic foods here you will need the skills of a health professional 
who's smart about food allergies and the use of laboratory immunoassays needed to help you discover what foods 
you're allergic to. 

Immediate food allergy involves foods that are rarely eaten. Unfortunately, delayed food allergy involves commonly 
eaten foods, foods that you eat every day and may even crave. 

When people quit eating foods that cause immediate symptoms, they have no withdrawal or detoxification 
symptoms. They don't crave or miss these foods. Powerful addictive cravings and disabling withdrawal symptoms are 
reported in over 30 percent of delayed food allergy patients when they stop eating  food. 

Immediate food allergens primarily affect the skin, airway and the digestive tract. Virtually any tissue, organ or 
system of the body can be affected by delayed food allergy. This  includes the brain, joints, muscles, 
hormone-producing  glands, lungs, kidneys, and nervous system. In fact, delayed-onset food  allergy is linked to over 
100 medical conditions involving every single part of the body and some 100 different allergic symptoms. 

Immediate-onset food allergies are frequently permanent and fixed allergies. Once you develop an allergy to 
peanuts or shellfish, for example, it's for life. Delayed-onset food allergies are commonly reversible. If you strictly 
eliminate the allergic foods for 3 to 6 months,  you can bring most of them back into your diet and remain 
symptom-free. Because delayed-onset food allergies are so often undetected and untreated, they lie behind many of 
chronic medical conditions of unknown cause. These allergic people suffer for years, even decades, without ever 
suspecting that their health problems  are rooted in what they eat. 

 Immediate-onset food allergy is often a skin-test positive allergy. The doctor can diagnose it with a simple skin test. 
 Delayed food allergies are skin-test negative. The traditional skin tests are poor tests for detecting delayed food 
 allergies. Instead, delayed reactions food often require state-of-the-art  blood tests. These tests detect serum levels 
 of  IgG antibodies to foods -- IgA antibody as well as IgG in gluten sensitivity and celiac disease. 

 Because delayed food allergies do not make themselves apparent immediately and can be caused by multiple 
 foods, they are very difficult to detect without sophisticated laboratory testing.  There are many forms of allergy testing available such as cytotoxic, computerized cytotoxic, applied kinesiology, vega tests, and others, but each of these 
 tests share the same critical disadvantage... they are frequently unreliable.