How should food allergies be tested in babies with siblings who have food allergies?

Testing for Food Allergies in Babies with Siblings Who Have Food Allergies

Routine preemptive screening or testing for food allergies is not recommended in babies whose only risk factor is having a sibling with food allergies. 1

Key Evidence on Sibling Risk

The evidence clearly indicates that having a sibling with food allergy does not substantially increase risk enough to warrant routine testing:

• International guidelines explicitly state there is no clear evidence that the younger sibling of a peanut-allergic child is at significantly increased risk of developing peanut allergy, though such infants may be at risk if peanut introduction is delayed 1

• One analysis notes that siblings of peanut-allergic children have only a "mildly elevated risk" and should be referred to an allergist for evaluation rather than routine testing 1

• The NIAID expert panel recognizes that many infants eligible for early peanut introduction will have older siblings with established peanut allergy, but this alone does not change the testing recommendations 1

When Testing IS Indicated

Testing should be reserved for babies who have actual clinical risk factors, not just family history 1:

• Severe eczema and/or egg allergy in the infant themselves - these babies should have evaluation before introducing peanut at 4-6 months 1

• Moderate-to-severe atopic dermatitis that persists despite optimized topical therapy 1

• Reliable history of immediate reaction after ingesting a specific food 1

• Infants younger than 5 years with persistent atopic dermatitis should be considered for evaluation for cow's milk, egg, peanut, wheat, and soy 1

The Recommended Approach Instead of Testing

Rather than testing based on sibling history alone, the evidence-based strategy is:

1. Introduce allergenic foods early (around 6 months, but not before 4 months) regardless of sibling history 1

2. For babies with no eczema or only mild eczema: introduce peanut-containing foods at home without any testing or in-office evaluation 1

3. Once introduced, maintain regular ingestion (at least once per week) to maintain tolerance 1, 2

4. No delays between introducing different allergenic foods - they can be introduced without waiting days between new foods 2

Important Clinical Pitfalls

• Do not confuse sensitization with allergy: A positive skin prick test or specific IgE in the absence of clinical symptoms does not diagnose food allergy 1

• Testing has poor positive predictive value: Simply having allergen-specific IgE does not indicate disease 1

• Unnecessary avoidance causes harm: One study showed 84-93% of foods avoided by children with atopic dermatitis could actually be tolerated when properly tested 3

• The risk of severe reaction at first exposure in infancy is extremely low, making preemptive screening unnecessary 2

Family Discussion Points

When a family has an older child with food allergy, discuss with parents 1:

• The overall benefit of introducing allergenic foods to the baby (reduced risk of developing allergy)
• Versus the risks of having that allergen in the home (potential for accidental exposure of the allergic sibling)
• This is a preference-sensitive decision that should be individualized based on the family's ability to safely manage having the allergen present 1

The bottom line: Having a sibling with food allergy alone does not warrant testing. Focus instead on early, regular introduction of allergenic foods starting around 6 months of age, with testing reserved only for infants who develop their own clinical signs of allergic disease.