Testing Siblings of FA Kids Yields False Positives

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SAN ANTONIO — Testing the siblings of food-allergic children for allergies is not advisable, new research suggests, because false-positive results could lead to food avoidance, which can increase the risk of developing an allergy down the road.

"Many children are sensitized to a food, so they will have a positive test result, but that does not mean they have a true food allergy," said lead researcher Ruchi Gupta, MD, from the Northwestern University Feinberg School of Medicine in Chicago.

The findings presented here at the American College of Allergy, Asthma & Immunology 2015 Annual Scientific Meeting are in agreement with current guidelines from the National Institute of Allergy and Infectious Diseases.

"Even though their test is positive," Dr Gupta explained, "they can still eat the food. We do not want kids unnecessarily avoiding food if they can eat it," she told Medscape Medical News.

The study — part of the Chicago Family Cohort food allergy study — involved 478 children with confirmed food allergy and 642 of their siblings.

Of the allergic children, about 50% were 2 to 5 years of age. Of the siblings, about 18% were 1 year or younger, about 40% were 2 to 5 years, and about 30% were 6 to 10 years.

  We do not want kids unnecessarily avoiding food if they can eat it. 
Caregivers completed detailed screening histories for both the allergic child and the siblings. Skin prick testing and serologic specific immunoglobulin E (sIgE) was performed on the siblings for cow milk, egg white, soybean, wheat, peanut, walnut, sesame seed, a fish mix, and a shellfish mix.

Food challenges, considered the gold standard test for food allergy, could not be performed, "so we developed a set of stringent criteria for symptoms reported within 2 hours of ingesting the food," Dr Gupta reported.

These symptoms included hives or angioedema, difficulty breathing, shortness of breath, repetitive coughing, wheezing or chest tightness, throat tightness, choking or difficulty swallowing, tongue swelling, fainting, dizziness, light-headedness or decreased consciousness, and vomiting.

Food allergy was defined as a positive skin prick test (mean wheal diameter, >3 mm) or positive sIgE (>0.35 kUA/L) plus clinical symptoms. Sensitization was defined as a positive skin prick test or positive sIgE with no clinical symptoms.

The researchers found that 34% of the siblings had no sensitization to foods and no clinical symptoms, 53% had sensitization to food, and 13% had an actual food allergy.

These symptoms included hives or angioedema, difficulty breathing, shortness of breath, repetitive coughing, wheezing or chest tightness, throat tightness, choking or difficulty swallowing, tongue swelling, fainting, dizziness, light-headedness or decreased consciousness, and vomiting.

Food allergy was defined as a positive skin prick test (mean wheal diameter, >3 mm) or positive sIgE (>0.35 kUA/L) plus clinical symptoms. Sensitization was defined as a positive skin prick test or positive sIgE with no clinical symptoms.

The researchers found that 34% of the siblings had no sensitization to foods and no clinical symptoms, 53% had sensitization to food, and 13% had an actual food allergy.

"Overall, 87% of the siblings had either a negative test or no symptoms," Dr Gupta reported.

Table. Common Allergies, Sensitizations in the Sibling Group

Outcome   Percent (n = 642)
Allergy   
   Milk   5.9
   Egg   4.4
   Peanut   3.7
Sensitization   
   Wheat   36.5
   Milk   35.4
   Egg   35.1
   Peanut   24.6
   Soy   23.1
   Tree nut   16.7
   Shellfish   14.8
   Fish   3.9


The researchers also looked at comorbid conditions, such as asthma and eczema, family history of allergies, hygiene factors (including having a pet in the home), infections in the first year of life, antibiotics, and cesarean delivery.

"We found that the only significant association with developing a food allergy in siblings was if they had asthma or eczema," said Dr Gupta.

Risk of Testing

It is important that physicians know what to do when parents of a food-allergic child ask whether their other children should be tested. "There is a lot of anxiety in the parent," said Dr Gupta.

Despite this worry, parents should be educated about the risk of testing, said Wade Watson, MD, head of the division of allergy at Dalhousie University in Halifax, Nova Scotia, Canada.

"Although parents are worried about siblings of allergic children, skin testing should not be routine because there is risk for false-positive tests, which are meaningless," he told Medscape Medical News.

However, "this needs to be balanced against parental concern and hesitation about introducing these foods to siblings," he added.

Dr Gupta and Dr Wade have disclosed no relevant financial relationships.

American College of Allergy, Asthma & Immunology (ACAAI) 2015 Annual Scientific Meeting: Abstract 36. Presented November 9, 2015.