Is it a food allergy or false alarm?

For Ingelisa Keeling, a Houston mother of three children with multiple allergies, mealtime was a struggle. Nuts, eggs, wheat, beef, peas and rice were all off limits — banned by the children’s allergist.

But recently, Mrs. Keeling learned that her family’s diet need not be so restrictive. Although her children do have real allergies — to peanuts, milk and eggs, among other foods — extensive testing at a major allergy center showed that they were not in fact allergic to many of the foods they had been avoiding. Her 2-year-old son, who had been living on a diet primarily of potatoes, fruit and hypoallergenic formula, has resumed eating wheat, bananas, beef, peas, rice and corn.

“His diet had become so, so restricted that nutrition had become a real concern,” said Mrs. Keeling, who traveled to specialists at National Jewish Health in Denver last summer for answers about her children’s diet and eczema problems. Among other findings, she learned that neither of her younger children was really allergic to wheat.

“That’s the big one,” she said. “Wheat is in everything, so it makes life a whole lot easier.”

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Doctors say that misdiagnosed food allergies appear to be on the rise, and countless families are needlessly avoiding certain foods and spending hundreds of dollars on costly nonallergenic supplements. In extreme cases, misdiagnosed allergies have put children at risk for malnutrition.

And avoiding food in the mistaken fear of allergy may be making the overall problem worse — by making children more sensitive to certain foods when they finally do eat them.

More than 11 million Americans, including 3 million children, are estimated to have food allergies, most commonly to milk, eggs, peanuts and soy. The prevalence among children has risen 18 percent in the past decade, according to the Centers for Disease Control and Prevention. While the increase appears to be real, so does the increase in misdiagnosis.

The culprit appears to be the widespread use of simple blood tests for antibodies that could signal a reaction to food. The tests have emerged as a quick, convenient alternative to uncomfortable skin testing and time-consuming “food challenge” tests, which measure a child’s reaction to eating certain foods under a doctor’s supervision.

While the blood tests can help doctors identify potentially risky foods, they aren’t always reliable. A 2007 issue of The Annals of Asthma, Allergy & Immunology reported on research at Johns Hopkins Children’s Center, finding that blood allergy tests could both under- and overestimate the body’s immune response. A 2003 report in Pediatrics said a positive result on a blood allergy test correlated with a real-world food allergy in fewer than half the cases.

“The only true test of whether you’re allergic to a food or not is whether you can eat it and not react to it,” said Dr. David Fleischer, an assistant professor of pediatrics at National Jewish Health. In one recent case there, doctors treated a young boy who had been given a feeding tube because blood tests indicated he was allergic to virtually every food. Food challenge testing allowed doctors to quickly reintroduce 20 foods into his diet, and they expect more to be added.

Blood tests may be unreliable because they fail to distinguish between similar proteins in different foods. A child who is allergic to peanuts, for instance, might test positive for allergies to soy, green beans, peas and kidney beans. Children with milk allergies may test positive for beef allergy.

The most important question in diagnosing food allergy is whether the child has tolerated the food in the past, Dr. Fleischer says. While some severe allergies are obvious, parents given a positive blood test result should seek advice from an experienced allergist who performs medically supervised food challenge testing.

Even when a food allergy has been confirmed, parents should have children retested, because many allergies are outgrown, particularly in the cases of milk, eggs, soy and wheat.

Doctors’ groups are also starting to acknowledge that some of their own policies may have contributed to overtesting and misdiagnoses. A committee for the American Academy of Asthma Allergy and Immunology is considering revised guidelines recommending earlier introduction of foods like eggs, peanuts and shellfish, which in the past have been delayed until age 2 or 3. A 2008 study of 10,000 British children, reported in The Journal of Allergy and Clinical Immunology, found that early exposure to peanuts lowered allergy risk.

Just as an allergy indicates oversensitivity to certain foods, it may be that doctors and parents have become oversensitive to food allergies. In an essay in The British Medical Journal in December, Dr. Nicholas A. Christakis, a professor at Harvard Medical School, argues that an “overreaction” to allergy is leading to unnecessary testing and false positives.

“If the kid has been doing fine, I would advise parents not to get allergy testing, because the results are more likely to be false positives than true positives,” Dr. Christakis said in an interview. “If they do think they need allergy testing, be extremely measured and go to reputable people.”