Peanut allergies less common than tests suggest

NEW YORK (Reuters Health) - Many children who test positive for sensitivity to peanuts may not actually have full-blown allergies to the food, a new study suggests.

UK researchers found that among 79 8-year-olds who were deemed peanut- sensitive by standard allergy testing, only 7 turned out to have true allergies when they underwent more-extensive testing that is less commonly used in routine practice.

As it stands, peanut allergy is typically diagnosed through a skin test, blood test or both.

During skin testing, the skin is pricked and exposed to a small amount of peanut protein to see if there is a reaction; blood tests, meanwhile, help diagnose peanut allergies by measuring levels of IgE antibodies, immune system substances that play an important role in allergic reactions.

The limitation of these two tests is that they gauge peanut sensitivity -- which refers to the immune system response to peanut proteins. But not everyone who is sensitive to peanuts has a true allergy, which means that a person has specific symptoms, like wheezing, hives, swelling or digestive problems, after eating peanuts.

This limitation becomes a problem when doctors are trying to diagnose a peanut allergy in a child with no clear history of symptoms, Dr. Adnan Custovic, the senior researcher on the new study, told Reuters Health in an email.

For example, parents often seek peanut-allergy testing when a child has allergies to other foods, or when they have another child with a peanut allergy, explained Custovic, who is with the University of Manchester.

But the current findings suggest that a majority of children who test positive for peanut sensitivity on standard tests do not have true allergies, Custovic and his colleagues report in the Journal of Allergy and Clinical Immunology.

The findings are based on skin tests and IgE blood tests of 933 8-year- olds, of whom 110 (12 percent) were deemed peanut-sensitized. Among those children, 12 had a "convincing history" of peanut-induced allergy symptoms, so they were considered to have a true allergy and no need for further testing.

Of the remaining children, 79 underwent food-challenge testing. Food- challenge tests are considered to be the definitive way to diagnose an allergy; under medical supervision, the patient eats food or takes a capsule containing the suspected allergen and is then monitored for an allergic reaction.

In this study, only 7 of the 79 peanut-sensitized children showed objective symptoms during the food challenge.

But while food-challenge tests are the "gold standard" for diagnosing peanut allergy, they are not a practical or routinely used option. The tests, Custovic noted, are time-consuming, expensive and carry the risk of causing a severe allergic reaction.

However, Custovic and his colleagues did find that a newer type of blood test may be more precise than standard IgE tests. The technique, called component-resolved diagnostics (CRD), involves exposing blood samples to specific, purified peanut proteins and measuring the IgE antibody response.

This is different from traditional IgE blood tests, which use "crude" peanut extracts that contain numerous allergenic and non-allergenic molecules, Custovic explained.

According to the researchers, CRD testing showed that the IgE response to a particular peanut protein, called Ara H 2, may prove useful in separating children with true allergies from those with a peanut sensitivity.

However, Custovic said, "it is important to emphasize that the findings need to be replicated" in other studies.

Sweden-based Phadia AB, which markets the CRD tests used in the study, provided some of the funding for the research. Several researchers on the study are Phadia employees, and Custovic has received lecture fees from the company.

SOURCE: Journal of Allergy and Clinical Immunology, January 2010.