According to researchers at National Jewish Health, many children, especially those with eczema, are unnecessarily avoiding foods based on incomplete information about potential food-allergies and as a result, are at risk for malnutrition and poor weight gain.

The food restrictions tend to be based primarily on data from blood tests known as serum immunoassays.

Immunoassays detect antibodies in the blood to specific foods, which can potentially cause allergic reactions. Interpretation of the results, however, can be tricky.

The tests' ability to predict true food allergy has been validated for only five foods - cow's milk, hen egg, fish, peanut and tree nuts. For all other foods, the numbers derived from lab testing are suggestive but not definitive.

Low test values suggest that a child's immune system is sensitized to the food, but not necessarily to the extent that it will cause an allergic reaction. Higher values suggest an increasingly likelihood of true food allergy.

None of the tests are 100 percent accurate, however, in predicting clinical food allergy on their own.

Many factors, including patient history, including any previous reactions to food, the type of reaction, the patient's age, family history, physical examination, and blood and skin tests, are used as evidence when evaluating potential food allergies. 

Doctors say the "gold standard” of food allergy tests is the oral food challenge, where the patient actually eats the suspected allergenic food. The oral food challenge is usually only performed when evidence is mixed and doctors want a definitive answer to the food allergy question.

Because of this, researchers found many kids are being denied foods that can only be determined allergenic based on the oral food challenge, putting them at risk for malnutrition and poor weight gain.

"People with known food allergies, especially those with a history of anaphylactic reactions, should by all means avoid those foods," said David Fleischer, MD, lead author of the study and Assistant Professor of Pediatrics at National Jewish Health.

"However, a growing number of patients referred to our practice are being placed on strict, unproven food-elimination diets that have led to poor weight gain and malnutrition. These overly restrictive diets have been chosen for a variety of reasons, but over-reliance on immunoassay tests appears to be the most common cause."

The researchers conducted a retrospective chart review of 125 children evaluated at National Jewish Health for suspected food allergies.

Children in the study were avoiding 177 different foods based primarily on previous blood test results.

In many cases, especially those with high test results for egg, milk, shellfish, peanut and tree nut, National Jewish Health elected not to perform oral food challenges.

They did perform oral food challenges for 71 foods or about 40 percent of the cases where the clinical allergy was equivocal and it was important to determine whether or not the patient had food allergy. In 86 percent of those cases, the child passed the food challenge and the food was restored to the child's diet.

Overall, 66 of the 177 foods avoided because of blood tests were restored to children's diets. For the entire study, 325 foods were restored to the diets of 125 children.

"When you are able to restore foods such as dairy products, egg, peanut, wheat, and vegetables to a child's diet, it improves their nutrition, reduces the need for expensive substitute foods and makes meal time easier for families," said Donald Leung, MD, PhD, senior author and Edelstein Chair of Pediatric Allergy and Clinical Immunology at National Jewish Health.

The problem can be especially acute among patients with eczema, also known as atopic dermatitis. Research suggests that specific foods can cause flare-ups in about one third of eczema patients. They commonly have high immunoassay tests to a variety of foods, many of which are not truly allergenic.

As a result, many mistakenly avoid foods they believe are causing flare-ups, but neglect basic skin care that is vital to improving the eczema. One hundred and twenty of the 125 children in the study had eczema.

The researchers published their study online in The Journal of Pediatrics on Oct. 29. It will appear in a later print version of the journal.