Ask an expert: Are high street allergy tests reliable?

Although high street allergy tests or home testing kits are easy to access, they are very unlikely to provide accurate results or much needed reassurance or advice about your child’s food allergy. In this informative article, highly experienced consultant paediatric allergist Professor George Du Toit expertly outlines how children’s allergies are tested and diagnosed. He also details the importance of taking a full clinical history in ensuring comprehensive care and preventing unexpected and potentially serious allergic reactions.

How are paediatric food allergies diagnosed by a specialist?

When testing for IgE-mediated food allergies, those which cause a reaction within a few minutes or after several hours of eating, there are only two scientifically proven methods: the skin prick test (SPT) and specific-IgE antibody testing, which is also known as immune-cap testing and was formerly called RAST testing. Additional to these methods, I make use of ISAC testing and IgE component testing in my own practice.

Additional to the testing method, a crucial element of diagnosis is taking a thorough clinical history. In my own practice, I always take a full history of any allergies and aversions to food. Establishing this is the first step as the patient’s history guides the testing to follow. For this reason, high-street tests are often unreliable as they usually do not involve a clinical history being taken.

Why is a taking a clinical history important?

There are several reasons why it is essential to take a full history when diagnosing an allergy. Very young children may refuse food which they are actually allergic to, meaning that a serious allergy to egg, for example, could be perceived merely as an aversion by the parents. In this way, taking a rigorous history enables the specialist to have a full picture of the child’s previous interactions with all types of foods.

Another aim of the history is to assess if the child is able to consume an age-appropriate amount of the food in question. If a non-allergic five year old child, for example, is able to eat a peanut butter sandwich, a whole egg, a slice of bread or a full glass of milk, they can be said to be tolerant to the food in question.

Additional to the history, a physical examination helps to establish if the child is growing well and can also allow the specialist to rule out an iron deficiency, rickets or any other nutritional issues. Assessing the condition of the child’s skin and breathing also helps to determine if any concomitant allergic conditions, including asthma or eczema, are at play.

Why are high-street tests unreliable?

High street allergy tests or those sourced online do not provide effective diagnosis or accurate testing of allergies. This is because they do not include a clinical history taken by a specialist and as such, usually involve testing against an endless list of potential allergens that the child most likely tolerates well. Taking a clinical history allows the specialist to identify likely possible allergens according to the child’s individual experiences.

Allergy testing by a specialist also includes establishing any co or cross allergies to other foods, especially if they have not yet been consumed by the child or if the child has reported a dislike of the given food.

Additionally, it is also important to identify any other allergens which can influence other allergic disorders, such as a pet dander allergy which acerbates the child’s asthma, for example. Factors such as this should be investigated as they can increase a child’s risk factor for more serious food-induced allergic reactions.

When is a screening allergen panel required?

In some cases, even after taking a detailed history, it isn’t possible to identify a candidate allergen and so a screening allergen panel is required. Although more wide-ranging, screening panels should not be open ended and should take into account the following factors:

• the patient’s age
• the allergic condition
• the geographical location

In many of such cases, young children’s allergies can be accounted for by testing for allergy to peanut, tree nuts, egg white and cow’s milk. If the child has not previously eaten or tolerated wheat, soya or kiwi, these may also be added to the screening panel. In adults and older children, fin-fish, shellfish, kiwi and sesame should also be added to the screening panel, unless there is full reassurance that the patient can tolerate these foods.

Professor George Du Toit is one of the country’s leading paediatric allergy specialists. If you are concerned that your child may be suffering from an undiagnosed allergy and wish to book a consultation with Professor Du Toit, you can do so by visiting his Top Doctors profile.