Diagnostic Approach to Food Allergy in Atopic Dermatitis
The best approach is a diagnostic food elimination diet for 4-6 weeks followed by oral food challenge under medical supervision—not immediate skin testing or IgE testing alone, as these only indicate sensitization and have poor positive predictive value (40-60%) for true food allergy. 1, 2
Why Elimination Diet is Superior
Food elimination (Option D) is the recommended diagnostic approach because skin prick tests and food-specific IgE testing alone cannot diagnose food allergy—they only demonstrate sensitization, which is present in 50-90% of patients who do not actually have true food allergy. 3, 1, 2
The Diagnostic Algorithm
First, optimize topical treatment before attributing symptoms to food allergy—ensure adequate topical corticosteroid potency and emollient use are maximized. 2
Obtain detailed history looking for consistent temporal correlation between specific food exposure and discrete eczema flares (not just chronic baseline dermatitis). 3
Consider limited testing only if indicated: In children <5 years with moderate-to-severe atopic dermatitis that persists despite optimized topical therapy, testing for cow's milk, eggs, wheat, soy, and peanut may be considered. 1, 2
Implement diagnostic elimination diet: Remove suspected foods for 4-6 weeks and monitor for improvement. 1, 2
Confirm with oral food challenge: This is essential because improvement during elimination may be coincidental or placebo effect—the double-blind placebo-controlled food challenge is the gold standard, though open challenges are acceptable in clinical practice. 3, 1, 2
Why Other Options Are Inadequate
Option A (Immediate Skin Test)
- Skin prick testing has high negative predictive value (>95%) but poor positive predictive value (40-60%). 2
- A positive test only indicates sensitization, not clinical allergy. 1, 2
- Cannot be used alone to diagnose food allergy. 3
Option C (IgE for Food)
- Food-specific IgE has the same limitation as skin testing—poor positive predictive value. 1, 2
- Positive IgE only reflects sensitization; clinical relevance must be established through elimination and challenge. 1, 2
- Basing elimination diets on positive IgE alone without clinical correlation is explicitly discouraged. 1
Critical Pitfalls to Avoid
Never start elimination diets based solely on positive skin tests or IgE without clinical correlation—this leads to unnecessary dietary restrictions that can cause weight loss, poor growth, calcium deficiency, hypovitaminosis, and kwashiorkor. 1, 2
Do not perform extensive allergy testing without clear medical history—positive results may only reflect sensitization rather than true allergy. 2
Avoid prescribing avoidance without treating the underlying atopic dermatitis—effective treatment remains skin care and topical therapies even when food allergy is confirmed. 2
Always confirm suspected food allergy with oral food challenge—presumptive diagnosis based on history and testing alone is no longer acceptable except in cases of severe anaphylaxis after isolated ingestion. 3, 4
When to Refer to Allergist
Referral is recommended for supervised oral food challenges, formulation of emergency anaphylaxis action plans, and longitudinal care to facilitate proper elimination diets and prevent unnecessary dietary restrictions. 2