Patterns of Illness: Food Allergies are a Whole-body Disease
Food allergy is a whole-body disease and a lottery selection of disturbances may evolve over many years. In many older children and adults we can trace the illness pattern back to infancy with slow, intermittent emergence of symptoms over several years. There may be intermissions of relatively good health lasting months to years. In other patients the illness begins abruptly and progresses rapidly without prior symptoms.
Food allergy is a whole-body disease and a lottery selection of disturbances may evolve over many years. In many older children and adults we can trace the illness pattern back to infancy with slow, intermittent emergence of symptoms over several years. There may be intermissions of relatively good health lasting months to years. In other patients the illness begins abruptly and progresses rapidly without prior symptoms.
How can I find out what foods I am allergic to?
Introduction:
As a child I battled severe environmental allergies, and minor food allergies to tree fruits (apples, peaches, pears, plums etc.,) and nuts (peanuts, etc.,). But as the years went by I learnt to cope with these reactions by finding alternative ways to consume them e.g. I ate canned fruit. And ate nuts in cereal or chocolate etc. But my first encounter with a major reaction occurred when I was in my early 20's.
Like most people at that age or a bit younger, I was on a pursuit to get fit. So I joined weight-loss program. One of the suggestions made was to replace regular low fat products with soy products, as they were higher in protein and lower in fat. So me being the adventurous person that I am went out and bought some soy pudding. That night after I opened the cup of the soy pudding and started analyzing it. The look and smell were fine, but little did I know that it was taste that would change my life forever. I scooped out a spoon full, and was about to put it in my mouth, when a little voice inside me said: "hey maybe I should try licking it first." I licked the top of the spoon, and within a matter of seconds I felt my lips, throat, tongue and cheeks swell to such an extent that I felt and looked like I had swallowed a basketball. Because of the severe swelling my airway passages had almost been blocked fully. So I began gasping for air, like someone drowning. If that wasn't bad enough I began coughing up phlegm, and vomiting. The vomiting brought along with it the nausea, stomach cramps, and feverish feeling/ chills. This went on for more than an hour, but I managed to battle it out with only one tablet of Benadryl and a puff from my inhaler. Little did I know that I had just experienced my first "Anaphylactic shock" reaction?
Diagnosing the onset of food allergies can be quite difficult. The help of a dietician is often needed. Tests, which are usually very time consuming will be carried out carefully. You will normally be asked to keep a record of what foods you have eaten over a period of weeks. This record will then be used to study if there is a relationship between the foods eaten and any symptoms experienced. The dietician will normally want to introduce you to a strict diet, known as an elimination diet. The foods your dietician chooses are based on those least likely to cause you an allergic reaction, such as chicken, lamb, pears, carrots, sprouts, rice and potatoes. This process involves your diet being monitored to see if you can settle on the chosen diet, then slowly adding additional foods to your diet. With this method, the source of the problem should be recognized when a reaction occurs.
One of the most difficult problems you will encounter when on an elimination diet is eating prepared food, as it may be difficult to know if they contain the offending allergen. You will need to read the small print on all labels. Now thanks to a significant improvement in food labelling it is possible to identify which foods contain the substances you personally need to avoid. Although this diet involves a great deal of effort and inconvenience, if you do discover an allergy then the removal of the offending item from your diet can make your life much more comfortable.
Diagnosing a food allergy - If you suspect that you have a food allergy, you should contact your GP who will help determine whether you have an allergy by taking a detailed case history of your reactions; so the more details that you can give, the better. Questions might include: How quickly did the reaction start after you ate the food? Did you take treatment for the allergy (eg antihistamines) and did it work? Do you always get this reaction to the food? How much of it did you eat this time? How was the food cooked and stored?There are also some tests which can be used to diagnose food allergies.
Elimination diets - Under the supervision of an allergy specialist, you remove the suspected allergy food from your diet and replace it with another food. For example, if your doctor suspects an egg allergy, you'd replace egg with a different food. If the allergy symptoms go away, a diagnosis can usually be made. To confirm this diagnosis, you may be asked to reintroduce the allergy food back into your diet. However, this is not safe if you've had severe allergy symptoms in the past, except under medical supervision at hospital.
TESTING Process:
Food Allergy Testing, by Dr. Adrian Morris.
The most commonly used diagnostic test in Food Allergy is Skin Scratch Testing with Food Allergens. Skin Scratch Testing is the cornerstone in allergy diagnosis, it has been used for over 100 years. Skin testing is cheap, safe, easy to do and someone in the practice can easily be trained to perform it. Commercial inhalant allergens are readily available, but food allergens are a little more difficult to come by. The main problem with food allergens is the lack of stability of extracts. A few food allergens such as Peanut, Egg, Wheat, Soya, Tree nuts, Fish and Cocoa are stable and commercial allergens are available. However, fruit and vegetable allergens are very unstable and rapidly denature rendering commercial extracts unreliable. Infants can be skin tested for food allergy from 4 months of age. For this reason, for fruit and vegetable allergens, we tend to use the Prick plus Prick test, where we prick the offending food, gather some sap and then prick the patient with the fresh extract.
This form of testing is highly reliable and possibly more accurate than RAST tests. When Skin or Prick plus Prick test are not available, RAST tests should be used - Many of the RAST fruit allergens extracts are labile and only have a 60% accuracy. They can also be very expensive and blood has to be sent to specialised immunology laboratories to be processed. The negative predictive value of food allergy testing is good - if a test is negative, then there is a 90% chance of there being no allergy to that food., but the positive predictive value is less specific - a positive test indicates sensitisation to that food but does not necessarily confirm a clinical allergic response will occur. The Double blind placebo controlled food challenge test is the gold standard for food allergy diagnosis, but is totally impractical in the GP setting as it can be very dangerous and trigger anaphylaxis. Only specialised allergy centres with in-house allergy dieticians and full resuscitation equipment are prepared to do this form of testing. Open food challenges (non-blinded) with the suspected food allergen is the more popular procedure in most clinics. Traces of the offending food are introduced to the person, initially by rubbing onto the skin. Then contact is made with the eye or lip. Next traces are placed on the oral mucous membranes, until finally a substantial amount of the food is consumed without reaction. These challenges take place under close medical supervision at 15-minute intervals. The test is aborted if an adverse reaction occurs at any stage. [edit] Role in disease
What Allergy tests are available?
The type of test to be carried out will depend upon your symptoms or condition of your skin and are described as follows.
Skin Prick Testing:
This is a test, which measures specific IgE attached to cells in the skin important in allergies called "mast" cells. This is probably the most commonly used allergy test and is appropriate for inhaled and ingested (eaten) allergies. It is usually carried out on the inner forearm (palm uppermost). If the patient has bad eczema on the area under test then the test can be performed on the back. Ideally the allergens to be selected should be in accordance with the patient’s history. As few as 3 or 4 or up to about 25 allergens can be tested. The arm is coded with a marker pen for the allergens to be tested and a drop of the allergen (extract) solution is placed by each code. The skin is then pricked through the drop using the tip of a lancet -this can feel a little uncomfortable but should not be painful.
Positive reaction:
The skin becomes itchy within a few minutes and then becomes red and swollen with a "weal" in the centre (very much like the reaction to a nettle sting). The weal has a raised edge, which slowly expands to reach its maximum size in about 15-20 minutes, clearing for most people within an hour. The size of the weal varies with the average being 3-5 mm in diameter.
Also included in skin testing is a negative and positive control:
The negative control is a saline (salt-water) solution, to which a response is not expected. If however a patient reacts to a negative control, then this will indicate that the skin is, for what ever reason, extremely sensitive and that the results from the allergen challenge needs to be interpreted with the utmost care.
The positive control solution contains histamine, to which everyone is expected to react. Failure to do so could mean that medicines the sufferer is taking could block the response to the histamine and allergens. Patients will be asked to avoid taking anti histamines, cough medicine and some anti depressants (Tricyclic) for about 5-6 days prior to the test.
The skin prick test introduces such a tiny amount of allergen into the skin that testing is quite safe and almost any age group can be tested. However where there has been a clear anaphylactic (shock) reaction to a specific allergen ingested then skin testing may not be appropriate. These tests can be carried out on all age groups including babies although the response will be considerably smaller than in an adult.
Skin prick testing is usually the first test recommended when an allergy is suspected. The advantages are that it is a simple, quick and inexpensive form of testing. It can give useful information in all forms of allergy and provides results within 15-20 minutes. This can be carried out within a hospital or GP surgery environment, by specially trained nurses or doctors.
Blood Test:
The test is carried out on a small sample of blood, which is usually taken from a vein in the arm, using a fine needle and a small syringe, causing minimal discomfort. The sample is then sent to a hospital laboratory and the results are available in 7 to 14 days. The blood sample can be taken at the GP surgery or at a hospital. These tests are particularly useful when:
The patient has a risk of an anaphylactic (shock) reaction, which would make skin prick testing too risky.
When extensive eczema makes skin prick testing impractical. When antihistamine medication cannot be stopped because of severe symptoms. No skin prick testing facilities are available Where unusual and rare allergens are suspected, as there are a wide range of UniCAP® allergens now available for testing
Positive Test: - UniCAP is reported in classes of 0-6 where increasing classes indicate increasing sensitivity to an allergen:
Class 0 Negative
1 Low
2 Moderate
3 High
4 –6 Extremely High
Source: http://www.internethealthlibrary.com/Health-problems/Allergies.htm#What%20are%20Allergies?
Patch Testing:
This test is performed in cases of contact dermatitis (Eczema) where allergy is suspected.
Any professional interpreting skin, blood or patch tests must first interpret the results in the light of the patient’s history. No test should be read in isolation.
Introduction:
As a child I battled severe environmental allergies, and minor food allergies to tree fruits (apples, peaches, pears, plums etc.,) and nuts (peanuts, etc.,). But as the years went by I learnt to cope with these reactions by finding alternative ways to consume them e.g. I ate canned fruit. And ate nuts in cereal or chocolate etc. But my first encounter with a major reaction occurred when I was in my early 20's.
Like most people at that age or a bit younger, I was on a pursuit to get fit. So I joined weight-loss program. One of the suggestions made was to replace regular low fat products with soy products, as they were higher in protein and lower in fat. So me being the adventurous person that I am went out and bought some soy pudding. That night after I opened the cup of the soy pudding and started analyzing it. The look and smell were fine, but little did I know that it was taste that would change my life forever. I scooped out a spoon full, and was about to put it in my mouth, when a little voice inside me said: "hey maybe I should try licking it first." I licked the top of the spoon, and within a matter of seconds I felt my lips, throat, tongue and cheeks swell to such an extent that I felt and looked like I had swallowed a basketball. Because of the severe swelling my airway passages had almost been blocked fully. So I began gasping for air, like someone drowning. If that wasn't bad enough I began coughing up phlegm, and vomiting. The vomiting brought along with it the nausea, stomach cramps, and feverish feeling/ chills. This went on for more than an hour, but I managed to battle it out with only one tablet of Benadryl and a puff from my inhaler. Little did I know that I had just experienced my first "Anaphylactic shock" reaction?
Diagnosing the onset of food allergies can be quite difficult. The help of a dietician is often needed. Tests, which are usually very time consuming will be carried out carefully. You will normally be asked to keep a record of what foods you have eaten over a period of weeks. This record will then be used to study if there is a relationship between the foods eaten and any symptoms experienced. The dietician will normally want to introduce you to a strict diet, known as an elimination diet. The foods your dietician chooses are based on those least likely to cause you an allergic reaction, such as chicken, lamb, pears, carrots, sprouts, rice and potatoes. This process involves your diet being monitored to see if you can settle on the chosen diet, then slowly adding additional foods to your diet. With this method, the source of the problem should be recognized when a reaction occurs.
One of the most difficult problems you will encounter when on an elimination diet is eating prepared food, as it may be difficult to know if they contain the offending allergen. You will need to read the small print on all labels. Now thanks to a significant improvement in food labelling it is possible to identify which foods contain the substances you personally need to avoid. Although this diet involves a great deal of effort and inconvenience, if you do discover an allergy then the removal of the offending item from your diet can make your life much more comfortable.
Diagnosing a food allergy - If you suspect that you have a food allergy, you should contact your GP who will help determine whether you have an allergy by taking a detailed case history of your reactions; so the more details that you can give, the better. Questions might include: How quickly did the reaction start after you ate the food? Did you take treatment for the allergy (eg antihistamines) and did it work? Do you always get this reaction to the food? How much of it did you eat this time? How was the food cooked and stored?There are also some tests which can be used to diagnose food allergies.
Elimination diets - Under the supervision of an allergy specialist, you remove the suspected allergy food from your diet and replace it with another food. For example, if your doctor suspects an egg allergy, you'd replace egg with a different food. If the allergy symptoms go away, a diagnosis can usually be made. To confirm this diagnosis, you may be asked to reintroduce the allergy food back into your diet. However, this is not safe if you've had severe allergy symptoms in the past, except under medical supervision at hospital.
TESTING Process:
Food Allergy Testing, by Dr. Adrian Morris.
The most commonly used diagnostic test in Food Allergy is Skin Scratch Testing with Food Allergens. Skin Scratch Testing is the cornerstone in allergy diagnosis, it has been used for over 100 years. Skin testing is cheap, safe, easy to do and someone in the practice can easily be trained to perform it. Commercial inhalant allergens are readily available, but food allergens are a little more difficult to come by. The main problem with food allergens is the lack of stability of extracts. A few food allergens such as Peanut, Egg, Wheat, Soya, Tree nuts, Fish and Cocoa are stable and commercial allergens are available. However, fruit and vegetable allergens are very unstable and rapidly denature rendering commercial extracts unreliable. Infants can be skin tested for food allergy from 4 months of age. For this reason, for fruit and vegetable allergens, we tend to use the Prick plus Prick test, where we prick the offending food, gather some sap and then prick the patient with the fresh extract.
This form of testing is highly reliable and possibly more accurate than RAST tests. When Skin or Prick plus Prick test are not available, RAST tests should be used - Many of the RAST fruit allergens extracts are labile and only have a 60% accuracy. They can also be very expensive and blood has to be sent to specialised immunology laboratories to be processed. The negative predictive value of food allergy testing is good - if a test is negative, then there is a 90% chance of there being no allergy to that food., but the positive predictive value is less specific - a positive test indicates sensitisation to that food but does not necessarily confirm a clinical allergic response will occur. The Double blind placebo controlled food challenge test is the gold standard for food allergy diagnosis, but is totally impractical in the GP setting as it can be very dangerous and trigger anaphylaxis. Only specialised allergy centres with in-house allergy dieticians and full resuscitation equipment are prepared to do this form of testing. Open food challenges (non-blinded) with the suspected food allergen is the more popular procedure in most clinics. Traces of the offending food are introduced to the person, initially by rubbing onto the skin. Then contact is made with the eye or lip. Next traces are placed on the oral mucous membranes, until finally a substantial amount of the food is consumed without reaction. These challenges take place under close medical supervision at 15-minute intervals. The test is aborted if an adverse reaction occurs at any stage. [edit] Role in disease
What Allergy tests are available?
The type of test to be carried out will depend upon your symptoms or condition of your skin and are described as follows.
Skin Prick Testing:
This is a test, which measures specific IgE attached to cells in the skin important in allergies called "mast" cells. This is probably the most commonly used allergy test and is appropriate for inhaled and ingested (eaten) allergies. It is usually carried out on the inner forearm (palm uppermost). If the patient has bad eczema on the area under test then the test can be performed on the back. Ideally the allergens to be selected should be in accordance with the patient’s history. As few as 3 or 4 or up to about 25 allergens can be tested. The arm is coded with a marker pen for the allergens to be tested and a drop of the allergen (extract) solution is placed by each code. The skin is then pricked through the drop using the tip of a lancet -this can feel a little uncomfortable but should not be painful.
Positive reaction:
The skin becomes itchy within a few minutes and then becomes red and swollen with a "weal" in the centre (very much like the reaction to a nettle sting). The weal has a raised edge, which slowly expands to reach its maximum size in about 15-20 minutes, clearing for most people within an hour. The size of the weal varies with the average being 3-5 mm in diameter.
Also included in skin testing is a negative and positive control:
The negative control is a saline (salt-water) solution, to which a response is not expected. If however a patient reacts to a negative control, then this will indicate that the skin is, for what ever reason, extremely sensitive and that the results from the allergen challenge needs to be interpreted with the utmost care.
The positive control solution contains histamine, to which everyone is expected to react. Failure to do so could mean that medicines the sufferer is taking could block the response to the histamine and allergens. Patients will be asked to avoid taking anti histamines, cough medicine and some anti depressants (Tricyclic) for about 5-6 days prior to the test.
The skin prick test introduces such a tiny amount of allergen into the skin that testing is quite safe and almost any age group can be tested. However where there has been a clear anaphylactic (shock) reaction to a specific allergen ingested then skin testing may not be appropriate. These tests can be carried out on all age groups including babies although the response will be considerably smaller than in an adult.
Skin prick testing is usually the first test recommended when an allergy is suspected. The advantages are that it is a simple, quick and inexpensive form of testing. It can give useful information in all forms of allergy and provides results within 15-20 minutes. This can be carried out within a hospital or GP surgery environment, by specially trained nurses or doctors.
Blood Test:
The test is carried out on a small sample of blood, which is usually taken from a vein in the arm, using a fine needle and a small syringe, causing minimal discomfort. The sample is then sent to a hospital laboratory and the results are available in 7 to 14 days. The blood sample can be taken at the GP surgery or at a hospital. These tests are particularly useful when:
The patient has a risk of an anaphylactic (shock) reaction, which would make skin prick testing too risky.
When extensive eczema makes skin prick testing impractical. When antihistamine medication cannot be stopped because of severe symptoms. No skin prick testing facilities are available Where unusual and rare allergens are suspected, as there are a wide range of UniCAP® allergens now available for testing
Positive Test: - UniCAP is reported in classes of 0-6 where increasing classes indicate increasing sensitivity to an allergen:
Class 0 Negative
1 Low
2 Moderate
3 High
4 –6 Extremely High
Source: http://www.internethealthlibrary.com/Health-problems/Allergies.htm#What%20are%20Allergies?
Patch Testing:
This test is performed in cases of contact dermatitis (Eczema) where allergy is suspected.
- The allergens are prepared in appropriate concentrations in white soft paraffin (e.g. Vaseline) and are then spread on to discs, 1 cm diameter.
- The discs (which are made of a special metal, cannot themselves provoke a reaction) are placed on the skin, usually on the back, and are kept in place by hypoallergenic tape.
The skin is coded appropriately and the patient is asked to keep the skin dry.- The patches are left in place for 48 hours, after which time the discs are removed, the skin is examined and any redness or swellings are noted. The skin is re-examined after a further 48 hours for any remaining local redness or swelling.
Any professional interpreting skin, blood or patch tests must first interpret the results in the light of the patient’s history. No test should be read in isolation.
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