Allergy Testing

Food allergies in children are increasing with up to 6% of children reacting to at least one food.  Most children grow out of their food allergies such as milk, egg, wheat and soy and many have grown out by school age.  Some foods such as peanut and tree nuts, however, can persist in up to 80% of children which causes considerable problems for them as they grow older. 

There are now some studies trying to determine whether early introduction of foods can delay or reduce the development of food allergies, but at the present time these studies have not been completed. 

What is clear is that in countries such as the United Kingdom where policies of prolonged avoidance were instituted that the incidence of certain food allergies such as peanut actually increased. 

There is evidence that sensitisation to foods can occur through the breast milk, through direct exposure with giving them foods directly and also sensitisation through the skin, particularly in children who have eczema.  Testing for food sensitisation can be done through blood test (RAST) or through a skin prick test (SPT) which, if done by properly trained personnel, can be very helpful and reliable.  There are criteria as guidelines for identifying those children at high risk of having reactions to foods as not all children who have positive skin prick tests will react to the food if they are exposed.  Skin prick testing, however, is a very useful way of monitoring and following changes as there is a correlation between the skin prick test result which measures the level of allergy antibody (IgE) in the skin and the development of tolerance which means growing out of the food allergy.  Unfortunately the skin prick test or the blood test is not able to determine the severity of any reaction, but is merely a guide as to whether you have a significant level of antibodies in your system.  We have no tests which can accurately predict what kind of reaction and, in particular, whether you are likely to have the severest form of reaction, which is anaphylaxis. 

The commonest foods that will cause problems in children will be cow’s milk, egg, peanut, tree nuts, soy, wheat and fish.  The types of reactions can vary significantly and some children can have mild reactions involving their skin whereas others can have more severe reactions involving their respiratory tract or cardiovascular system (anaphylaxis).  There are a number of children who have gastrointestinal sensitivity or intolerance to certain food proteins such as cow’s milk or wheat and they will present with symptoms such as vomiting, gastro-oesophageal reflux, irritability, sleep disturbance, colic, abdominal bloating, diarrhoea and constipation.  There have been a number of gastrointestinal disorders described around food reactions, particularly cow’s milk. 

There has been greater understanding of food allergy over the past 20 years, but there is still a lot to learn.  We are still unsure as to what causes sensitisation to foods in the first place and why and how the body switches off the production of allergy antibodies or the reason why you develop tolerance to certain foods.  It is likely to take many years before these questions will be answered, but there is considerable research going on around the world at the present time and the next 5-10 years promises to be very exciting in understanding further about food allergies.