Diagnosing your child's food allergy
Your healthcare professional should use the information about your child's symptoms and medical history to decide whether allergy tests are appropriate and, if so, which type of test would be suitable. This depends partly on the type of allergy they suspect.
Types of food allergy
There are two types of food allergy. The type depends on whether or not the allergic reaction is triggered by an antibody called immunoglobulin E (usually called IgE). These antibodies are the chemical signals that set off an acute (sudden) allergic reaction.
In an IgE-mediated food allergy, reactionsusually happen within a few minutes of eating the food. Common symptoms are reddening of the skin, an itchy rash, and swelling of the lips, face or around the eyes. A rare but more serious reaction is anaphylaxis (described in 'What will happen when we see a healthcare professional?').
The other type of food allergy is called a non-IgE-mediated food allergy. This type of allergy is not caused by IgE antibodies (it is usually because of cell reactions in the immune system).Non-IgE-mediated reactions often appear several hours or days after the food is eaten and can cause symptoms over a longer period, such as eczema, diarrhoea, constipation and, in more severe cases, growth problems.
Sometimes children have a mixed reaction which causes both IgE and non-IgE symptoms and signs (for example, this happens in some children with cows' milk allergy).
Your healthcare professional should consider your child's symptoms, medical history and assessment as well as the results of their tests when deciding if they have a food allergy.
If your healthcare professional thinks your child has an IgE-mediated food allergy they should offer your child either a blood test or a skin prick test. In a skin prick test, a small drop of liquid containing a suspected food protein is placed on the forearm, and then a tiny prick is made in the skin through the drop to see if a reaction happens. Your healthcare professional should explain exactly what these tests involve and talk to you about which test you and your child would prefer. Your child should not be offered a test called an atopy patch test without being seen by a specialist. You should not be advised to try a procedure called an oral food challenge, or be offered this procedure, without seeing a specialist if your child has suspected IgE-mediated food allergy.
Your healthcare professional should consider your child's symptoms, medical history and assessment as well as the results of their allergy tests when deciding if they have a food allergy.
If your healthcare professional thinks your child has a non-IgE-mediated food allergy they should discuss with you trying avoidance of the food for a trial period (usually between 2 and 6 weeks) and then reintroducing the food. This is known as an elimination diet. It may involve avoiding just one food, or several foods. If your child's symptoms improve or disappear when a food is avoided, but then return when that food is eaten again, it can confirm the allergy.
You and your child should be offered help and advice before you start an elimination diet. This should include how to understand food labels to make sure your child doesn't eat the suspected food by mistake, what foods they can eat instead to make sure they have a healthy diet, and how to reintroduce the food safely. Your healthcare professional should also take into account whether your child's culture or religion affects foods that they can or cannot eat.
You should be offered support from a dietitian if you need it, to help you start the elimination diet and check how you are managing.
Some complementary or alternative health practitioners offer tests for food allergy. These can include tests called applied kinesiology, hair analysis, vega tests and serum-specific IgG antibody tests. Your healthcare professional should not offer your child these tests because there is no evidence that they can reliably diagnose food allergy.