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Peanut Allergy Testing, Without the Nuts

Skin- and blood-based tests are safer and just as accurate, study finds

FRIDAY, June 10, 2005 (HealthDay News) -- Taking the peanut out of peanut-allergy testing, a British team has found that screening kids using just skin pricks and blood samples is accurate and safe; cutting the need for potentially dangerous food-sample tests.

Currently a "food challenge" -- in which a patient is offered a sample of the very food to which he or she might be allergic -- is considered the most reliable means by which to test for food allergies.

However, reporting in the June issue of the Journal of Allergy & Clinical Immunology, the authors point out that this traditional screening method always carries the risk of provoking a severe allergic reaction, or anaphylactic shock, among very allergic children.

"This study looks at some other testing options which can provide good information, so it's very helpful," said Dr. Clifford W. Bassett, an attending physician in the department of allergy and immunology at The Long Island College Hospital in Brooklyn, N.Y.

"Anytime we get more information regarding the millions of people who have peanut allergies, it's a great day," he said.

According to the National Institute of Allergy and Infectious Diseases, out of the more than 50 million Americans with some kind of allergy, approximately 3 million suffer specifically from either peanut or tree nut allergies.

The British researchers noted that 8 percent of infants are allergic to some form of common food, with peanuts ranking number one. Peanut allergy means the individual is allergic to proteins found in fresh, cooked and roasted peanuts.

Exposure to peanuts in any of these forms can provoke a wide range of reactions among those who are allergic. Mild symptoms are typically confined to itchy rashes, tingling in the mouth area, stomach pain, diarrhea and a generalized feeling of malaise. More severe symptoms, however, can include swelling of the face, impaired breathing, and collapse.

With such symptoms in mind, Dr. Graham Roberts and Dr. Gideon Lack, of the Department of Pediatric Allergy at St. Mary's Hospital, London, teamed up to explore the screening potential of tests that could confirm food allergy without the risk of food exposure.

They focused on 157 boys and girls under the age of 16 who were suspected of having a peanut allergy. All the patients were first screened in the traditional way, ingesting peanuts in increasing doses over 20 minute intervals until an allergic reaction, if any, became evident.

The researchers then performed forearm skin prick tests and/or took blood samples. Blood samples were analyzed for the elevated presence of peanut-sensitive types of immunoglobulin E, or IgE. Food-specific IgE antibodies are produced by the immune system and help instigate an allergic reaction if a particular allergen is detected.

When compared to traditional the food-challenge test, the skin prick and blood test screenings were able to accurately diagnose a childhood peanut allergy 95% and 92% of the time, respectively, the researchers report.

Although skin prick and blood tests are not new diagnostic options for allergy screening, Roberts and Lack said these methods have often been viewed as less reliable and conclusive than food-exposure tests.

To deal with this problem, the researchers raised the bar in terms of the reaction or IgE level needed for a peanut allergy diagnosis gleaned from a skin or blood test.

Skin prick reactions, for example, had to be at least 8 millimeters in diameter to be considered solid evidence of a peanut allergy.

Experts say the findings solidify the reliability of non-food-based testing.

"This is really a confirmatory study, more than brand-new information," said Dr. Scott H. Sicherer of the Jaffe Food Allergy Institute at Mount Sinai Hospital in New York City. "These are existing tests. It's not like this is a new test being done."

But Sicherer added that the study's focus on setting diagnostic minimums is helpful in developing more accurate allergy testing.

"It's important, because you can have an allergy test that is positive but the patient might still not have a problem eating a peanut," said Sicherer. "So what they found is that if the skin test is particularly large, or if you could measure a particularly high amount of the peanut IgE antibody in the blood, that makes it highly likely that the person affected would react to peanut."

Bassett cautioned, however, that its too soon to write off the traditional food-sample tests.

"They found that both of these tests were helpful, but it does not take the place of what's still considered the 'gold standard,'" said Bassett. "If you can tolerate the food and you don't have a negative reaction, then that speaks for itself. So the food challenge can still be very important, and if you don't do a food challenge you might miss something. Which is why a consultation is very, very important. The physician can make a decision with the family and the patient as to what tests to conduct."

More information

For more on peanut allergy and other food allergies, check out the The Food Allergy and Anaphylaxis Network.

SOURCES: Clifford W. Bassett, M.D., department of allergy and immunology, The Long Island College Hospital, Brooklyn, N.Y.; Scott H. Sicherer, M.D., Jaffe Food Allergy Institute, Mount Sinai Hospital, New York City; June 2005 Journal of Allergy & Clinical Immunology
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