FOOD ALLERGIES

Food allergy. What is it

The scientific definition of food allergy is that of an "adverse reaction to foods mediated by an immunologic mechanism." The difference compared to so-called intolerances is that in the latter, the mechanism is different. For example, lactose intolerance is not an allergy because responsible for this disease is very frequent in adults and children older, is a defect in the digestion of lactose, milk sugar, due to losses, with age, the substances (enzymes) that allow the digestione.Meccanismo immunological means that the food is able to determine the body (this is usually of people with a genetic predisposition) a series of processes (production of specific antibodies, activation of cells Particular etc.) which then hesitate in a reaction of various kinds. Depending on the type of mechanism responsible for the reactions may be immediate, even dangerous, such as anaphylactic shock (mechanism of type I or IgE mediated reactions) or slow, delayed, less violent, such as many gastrointestinal diseases (type mechanism IV or cell-mediated reactions.)
In the age pediatric are important both types of reactions: the first, of course, because potentially dangerous for life and therefore in need of multiple special attention, the latter because they represent a large share of allergy problems of the infant (persistent diarrhea, modest growth, insomnia, constipation, colic, gastroesophageal reflux, in part atopic dermatitis) and, as will be seen below, do not allow to use tests for the diagnosis of laboratory and instrumental. The only exception is the gluten intolerance or celiac disease, cell-mediated allergy, which provides for the possibility of a laboratory diagnosis by determining the serum of patients with specific autoantibodies (transglutaminase, endomysial, gliadin).

What are the symptoms

Allergies to foods are more frequent in pediatric patients as they are in adults. Are particularly present in the very young child, the first year of life and then decreased gradually with age. For example, the allergy to cow's milk, the most common of food allergies, disappears in half of the cases after a year of diagnosis and after three years 80% of children who had milk allergy acquire tolerance, although , sometimes, skin tests or blood remain positive. Instead, they tend to persist over the years and pesce.I peanut allergy symptoms with which it is manifested food allergy are varied and can affect various organ systems: the skin, the respiratory system, gastrointestinal tract, the nervous system, the cardiovascular system. For this reason we use to define allergy to food, "the great chameleon."
Of the many diseases that can be associated with allergy to some foods are definitely correlated to such an allergy, for others the role of food allergy in their origin is doubtful and sometimes unlikely, at least not scientifically proven.
way as was discussed and sometimes still is discussed on the role of food in the origin of certain diseases such as migraine syndrome hyperactive child with attention deficit disorder, the 'catarrhal otitis media, it is not scientifically proven that they are the cause of it.
Conversely certain is the role of food in some forms of urticaria (but not all!), some forms of atopic dermatitis (but not all!) in many cases of asthma, rhinitis, persistent cough, chronic diarrhea, failure to thrive, caught with the issue of blood in the stool. Finally, although not always and in every case related to food allergy in childhood such an allergy is the most common cause of what is usually called anaphylactic shock but that would be more appropriate to simply define anaphylaxis or anaphylactic shock because, that is, the participation of the cardiovascular crisis, it is not necessarily always present. The most common cause of anaphylaxis in children are therefore the food and especially the food most frequently responsible for, nor is fish. Also frequently anaphylaxis milk, egg, peanuts.

How is it diagnosed

And 'This is a very important topic. The diagnosis of food allergy is not easy and requires specific skills to prevent, as often happens, children are labeled as allergic or vice versa, although it had the allergy is excluded merely on the basis of test negativi.Vanno kept in mind two fundamental concepts:
1. Laboratory tests (RAST) and skin tests (Prick) are based on the finding, in the blood or on the skin, of a particular type of antibody (the so-called specific IgE) that may be responsible for allergic reactions so-called type I or, in fact, IgE mediated;
2. Have blood and skin these specific IgE (ie be sensitized to a food) does not necessarily mean that the assumption of certain food allergic reaction occurs. In other words the sensitization does not necessarily mean allergy.

The consequences of these two concepts, as mentioned fundamental, are many:
A. A negative test, prick or RAST it does not exclude that type of allergy is not linked to specific IgE. In other words, the negative tests do not exclude the so-called cell-mediated allergy, delayed, often of interest gastrointestinal. Going even more in detail if a child, for example, has not RAST positive or positive skin prick for milk that is not meant that its persistent diarrhea, its poor growth, its habitual vomiting, its atopic dermatitis is not due to ' intake of this food. E 'therefore not useful and wrong in these cases to predicating the diagnosis and the resulting milk-free diet and derived from the results of the tests. What is decisive in these cases is the practical test: that is practically suspend milk and its derivatives from the usual diet of the child and it is noted whether the symptoms that prompted the suspicion improve or disappear (test deletion).
B. A positive test, prick or RAST that is, to a certain food does not mean that the child has true authentic reactions to the food. It is often observed in daily practice, that children who have always assumed, with no real problems, foods such as milk or egg or wheat or tomato or whatever, the suspension is imposed because of these same foods, often for reasons entirely fanciful, were performed of allergy tests that are then positive results. Positivity does not necessarily mean allergy.
exist for the various different foods "positive predictive value" (PPV), that is, different statistical probability that a positive test corresponds to a true adverse reaction intake of food. This VPP is greater for example for peanuts but very low, for example, for the grain. This means that if a child has a positive test for the grain is more likely that in reality the child can safely assume the grain without problems, rather than the face, somehow, wrong. It 's always necessary, therefore, in these cases, before defining the child allergic to wheat and torment him with useless diets, try testing practices by improvement of problems with the suspension of the food and their subsequent reappearance to his risomministazione (test elimination and tolerance tests or provocation or challenge). For milk the positive predictive value is less than 50%: in other words, less than half of children with positive skin tests or RAST for milk has a tolerance to food is not authentic.

Are useful "allergy tests"?

If a negative test does not exclude the presence of allergy and a positive test does not necessarily mean allergy is useless to perform allergy testing for food No, it is not useless. We must of course know the significance and limitations. One should not rely completely on it for the management of the child. You should not treat the allergy test but: the test and should be considered a support, a diagnostic aid with different significance depending on the medical history of the child, presenting symptoms, how intense is the positivity of it.
history medical (history) of the child, family and staff is essential. According to it comes the suspected diagnosis. This diagnostic suspicion must be supported by specific skills that make it possible to speculate whether or not the motive of certain allergic symptoms. The doctor needs to know, for example, that it is very unlikely that a persistent diarrhea or poor growth in a child who is aged over two years may be due to food allergy, milk in particular, as well as should know that not all eruptions skin that your child has are due to "allergy" but that basically just hives and atopic dermatitis, which have very characteristic clinical picture, they can, but not always the case, be due to food allergy. Conversely, it is extremely common to see babies fed in an increasingly restrictive for skin diseases the most diverse and quite far from those two diseases.
Once the medical authority has considered compatible with a condition of food allergy symptoms that your child has is justified to perform or face testing purposes, but it is imperative that you consider the limitations in their interpretation of them and above all be equipped with common sense. Obviously it is much more likely that the test expresses a true allergy how much more the result is positive and vice versa. The values ??of RAST <3.5 kU / l or a modest positive (ES +) to the skin test more difficult are predictive of a true allergy; vice versa, the higher will be the values ??the more easily the children will be truly allergic to the food. Were from various experts in the field developed the threshold values ??of the test for milk, egg, wheat, fish, above which there is practically certain that that food is harmful to the child.
D 'On the other hand in diseases such as atopic dermatitis, poor growth, diarrhea, asthma, your doctor should know that the test does not exclude allergy to milk or other food could they be linked to a mechanism that is not provides for the intervention of specific IgE. In these cases, therefore, be other parameters, the age of the child (essential!) Familiarity, the coexistence of other symptoms, the failure to respond to appropriate treatment, to suggest that the food may be important.
For all these reasons , in any case, it should be stressed that the real test for the diagnosis of food allergy in children, are positive or not blood tests and skin tests, is the test of removing the food for one or two months and its subsequent reintroduction. It can then assess whether that really given disorder was linked to that certain food through its disappearance before and after its reappearance, at the time in which the food is reintroduced.