At what age should food allergy testing be done for babies with a high risk of allergy?

Food Allergy Testing in High-Risk Infants

For babies at high risk of food allergy (those with severe eczema or egg allergy), food allergy testing should be performed between 4-6 months of age, specifically before introducing peanut-containing foods, using skin prick testing rather than serum IgE measurement. 1

Defining High-Risk Infants

High-risk infants are those with:

• Severe eczema requiring topical corticosteroids or calcineurin inhibitors for at least 12 of 30 days on two occasions 1
• Egg allergy diagnosed in the first 4-6 months of life 1
• Either condition warrants evaluation by an allergist before introducing peanut 1

Testing Protocol for High-Risk Infants

When to Test

• Between 4-6 months of age, before introducing peanut-containing foods 1
• Testing should occur when the infant is developmentally ready for solid foods but before home introduction of peanut 1

Preferred Testing Method

• Skin prick testing (SPT) is preferred over serum IgE measurement because IgE testing results in considerably higher rates of sensitization, leading to unnecessary oral food challenges 1
• SPT should be performed with both negative and positive histamine controls, in duplicate, with the maximum wheal diameter measured 1

Interpreting Results and Next Steps

For peanut SPT results:

• Wheal ≤2 mm: Low allergy risk—introduce peanut at home or in office based on family/physician preference 1
• Wheal 3-7 mm: Moderate to high risk—supervised feeding in office or oral food challenge recommended before home introduction 1
• Wheal ≥8 mm: High likelihood of allergy—infant should remain under subspecialist care for assessment and monitoring 1

Important Caveats

Testing Is NOT Recommended for:

• Infants with mild-to-moderate eczema: These infants can introduce peanut-containing foods at approximately 6 months at home without pre-testing 1, 2
• Standard-risk infants without eczema or food allergies: No testing needed; introduce allergenic foods with other complementary foods around 6 months 1, 2
• Pre-emptive screening in all high-risk infants: While testing may be preferred by some families, it is not universally required 3, 4

Common Pitfalls to Avoid

• Do not use serum IgE as the primary screening tool in this age group, as it leads to overdiagnosis and unnecessary dietary restrictions 1
• Do not delay testing beyond 6 months in high-risk infants, as this misses the optimal window for early introduction (4-6 months) that provides the greatest protective benefit 1
• Do not test for multiple food allergens routinely—the evidence specifically supports testing for peanut in high-risk infants; other allergens can be introduced without testing 1, 4

After Testing: Introduction Strategy

Once testing is complete and the infant is cleared for introduction:

• Introduce peanut between 4-11 months of age in an age-appropriate form (smooth peanut butter mixed with milk/fruit, or softened peanut snacks) 1
• Maintain regular consumption (median 7.7g peanut protein per week was used in the landmark LEAP trial) to sustain tolerance 1
• Continue breastfeeding alongside solid food introduction 2, 5
• Introduce other allergenic foods (egg, dairy, wheat) around the same time without additional testing 1, 2

The Evidence Behind This Approach

The 2017 NIAID guidelines reversed previous recommendations after the LEAP trial demonstrated that early peanut introduction reduced peanut allergy risk by up to 80% in high-risk infants 1. This Level 1 evidence from a randomized controlled trial fundamentally changed practice, with subsequent endorsement by the American Academy of Pediatrics in 2019 and a 2021 consensus from the AAAAI, ACAAI, and Canadian Society for Allergy and Clinical Immunology 1, 4.

The key insight is that testing serves to stratify risk and guide the setting of introduction (home vs. supervised), not to determine whether to introduce the food at all—delaying introduction increases allergy risk 1.