Parents of a child with a food allergy are often concerned that their other children are at high risk for allergies, and may take them to the doctor to be screened with a blood test or skin prick.
Yet such siblings have only a slightly higher risk than the general population, about 13 percent compared with 8 percent, according to new research presented last week at the annual meeting of the American College of Allergy, Asthma & Immunology in San Antonio. And more than 50 percent of the siblings had a positive test but no actual food allergy. With that in mind, the authors say, we should limit testing siblings with blood and skin prick tests.
“A large proportion of these parents are unnecessarily avoiding a food their child could eat,” says Ruchi Gupta, lead author on the study and an associate professor of pediatrics at Northwestern University Feinberg School of Medicine.
False positives cause unnecessary stress and fear for parents and children, and, somewhat paradoxically, could increase the risk of a real allergy: Avoiding a potential allergen may increase the risk of developing food allergies later in life. A major study earlier this year, for example, found that exposing infants to peanuts before the age of 1 significantly lowered their risk of developing an allergy to the nuts in the future.
For the sibling study, Gupta and colleagues tested 1,120 children, from birth to age 21, with blood tests and skin pricks, then assessed true food allergy based on those tests plus the child’s history of reacting to the food. Among siblings of children with a food allergy, 33 percent tested negative for an allergy.
Of the remaining two-thirds who tested positive, only 13 percent had a true food allergy, most commonly to milk or egg. The remaining 53 percent of the siblings tested positive yet had no actual allergy. Those results are in accord with a 2013 Australian study that found having an immediate family member with a food allergy only modestly increased an infant’s allergy risk.
If parents are worried about allergies in a sibling, she recommends discussing concerns with an allergist and potentially following up any positive blood test or skin prick with a food challenge that can be performed safely in their office. “You can try it in a safe environment and make sure the child does or does not [have an allergy], so they can keep the food in their diet if possible.”