CENTER ON BEHAVIORAL MEDICINE
ADDITIONAL MATERIALDIAGNOSTIC TESTING
given by the author to reproduce this paper:
James Braly, M.D.
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:
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.
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:
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.
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.
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
tend to be more immediate and can be life-threatening. Common symptoms
Symptoms of food intolerance
Symptoms of food intolerance may
but are often delayed and are triggered only after a threshold level of
exposure is reached. They can include:
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
by a reaction to food, including:
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
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
area of research. Findings to date indicate that:
Food allergy - the common culprits
About 90 per cent of allergies
by nuts, eggs, milk or soy. Peanut allergy is one of the most common
in older children. Other foods that cause allergies include (in order
the most common):
Food intolerance - the common culprits
The foods that tend to cause
reactions in sensitive people include:
Tracking down the allergen
In most cases, symptoms appear
few minutes of eating the particular food, which makes pinpointing the
allergen an easy task. However, if the cause is unknown, diagnostic
may be needed such as:
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
certain substances in foods and certain foods including:
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
used to describe these foods on foods labels, for example:
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
allergy, immediate food allergy is common in children, but rare in
Allergic symptoms in immediate
occur within two hours of eating. Allergic symptoms in delayed
Immediate-onset food allergy
or two foods in the diet, as a rule. Delayed reactions
Because a small amount of a
is involved and the allergic symptoms appear immediately,
Immediate food allergy involves
are rarely eaten. Unfortunately, delayed food allergy involves
When people quit eating foods
immediate symptoms, they have no withdrawal or detoxification
Immediate food allergens
the skin, airway and the digestive tract. Virtually any tissue, organ
Immediate-onset food allergies
permanent and fixed allergies. Once you develop an allergy to
allergy is often
a skin-test positive allergy. The doctor can diagnose it with a simple
Because delayed food
not make themselves apparent immediately and can be caused by