Children's Health: Skin test signals which kids will lose peanut allergy

Regular skin tests can help predict which children with a peanut allergy will eventually grow out of it, Australian researchers have found.

About one-fifth of peanut-allergic children will stop reacting to the food over time, but there's no obvious sign this has happened. Dr. Katie Allen and her colleagues at the Royal Children's Hospital in Melbourne have found that measuring the size of the skin swelling, or wheal, that results from a skin allergy test can help identify children who may outgrow their allergy.

In a skin allergy test, the skin is pricked with a needle containing a small amount of the allergy-causing substance. If a skin reaction occurs, the child may be allergic to that substance.

The Melbourne team gave annual skin allergy tests to 267 children who had been diagnosed with peanut allergy by the time they were two years old.

The children who had larger skin prick test wheals at the beginning of the study were two to three times more likely to have persistent allergy compared with those whose wheals were smaller. Also, if the wheal size grew with each test, a persistent allergy was more likely, but if it shrank, the child was more likely to outgrow the condition. "The long-term prognosis to peanut could be easily predicted by the directional change of skin prick test wheal size, particularly by the age of three," Allen says.

By age five, 21 per cent of the children had become tolerant to peanut -- a figure Allan says is comparable to what's been seen in other studies.