What is the most appropriate investigation to evaluate a suspected food allergy in a child with atopic dermatitis refractory to emollients and low‑dose topical corticosteroids?

Supervised Food Challenge is the Most Appropriate Investigation

In a child with suspected atopic dermatitis refractory to emollients and low-dose topical corticosteroids where food allergy is suspected, supervised oral food challenge is the most appropriate investigation to confirm the diagnosis. 1, 2

Why Supervised Food Challenge is the Gold Standard

The American Academy of Dermatology explicitly recommends a diagnostic elimination diet (4-6 weeks) followed by oral food challenge under allergist guidance as the best approach to diagnose food allergy in atopic dermatitis not responding to topical steroids. 1 This two-step process is essential because:

• Improvement during elimination may be coincidental or placebo effect, making confirmation through challenge mandatory before imposing long-term dietary restrictions 1, 2
• Double-blind placebo-controlled food challenge (DBPCFC) is the gold standard, though open-label challenges are acceptable in clinical practice 1, 3
• The challenge should evaluate skin status using established scores (SCORAD or EASI) at 24 hours and later 2

Why IgE Testing and Skin Prick Tests Are Insufficient

Poor Positive Predictive Value

• Skin prick testing and food-specific IgE have only 40-60% positive predictive value and merely indicate sensitization, not true food allergy 1, 2, 3
• The American Academy of Dermatology states that 50-90% of presumed food allergies based on symptoms or positive tests are not true allergies 1
• Positive tests (≥0.35 kU/L for IgE or ≥3mm wheal for SPT) require correlation with clinical history and oral food challenge to confirm clinical allergy 4, 3

High Negative Predictive Value

• While these tests have >95% negative predictive value (useful for ruling out allergy), their poor positive predictive value means they lead to overdiagnosis when used alone 2, 3
• The National Academies consensus report emphasizes that equating a "positive test result" to having an allergy is a serious misconception 4

The Correct Diagnostic Algorithm

Step 1: Optimize Topical Therapy First

Before attributing symptoms to food allergy, ensure the child has received:

• Appropriate-potency topical corticosteroids (not just "low dose")
• Adequate emollient use
• Many children have inadequately treated atopic dermatitis, not food allergy 2

Step 2: Consider Limited Testing (Optional Screening)

If the child is under 5 years with moderate-to-severe disease persisting despite optimized treatment:

• Consider limited testing for milk, eggs, wheat, soy, and peanuts 1, 2
• Keep a food diary for one month to establish temporal correlation 2
• Remember: only 35% of children with moderate-to-severe atopic dermatitis have IgE-mediated food allergy 2

Step 3: Elimination Diet

If testing suggests sensitization or history is suggestive:

• Eliminate suspected foods for 4-6 weeks 1, 2
• This step alone cannot confirm diagnosis

Step 4: Supervised Oral Food Challenge (MANDATORY)

• Must be performed under allergist guidance with emergency equipment available 4, 1, 3
• Begin with minute amounts and stop at first symptoms 4
• This is the only way to confirm clinical relevance of suspected food allergy 1, 2, 3

Critical Pitfalls to Avoid

Nutritional Harm from Unnecessary Restrictions

The American Academy of Dermatology warns that excessively restrictive diets based on positive tests alone can cause:

• Weight loss and poor growth
• Calcium deficiency
• Hypovitaminosis
• Kwashiorkor 1, 2

Failure to Treat Underlying Dermatitis

• Often avoidance is prescribed without treating the underlying atopic dermatitis, which is incorrect management 2
• Effective treatment remains skin care and topical therapies, even with confirmed food allergy 2

Basing Elimination on Tests Alone

The American Academy of Dermatology advises against basing elimination diets on positive skin tests or IgE alone without clinical correlation and subsequent challenge confirmation 1, 2

When to Refer to Allergist

Referral is essential for:

• Longitudinal care and diagnostic testing 2
• Formulation of emergency anaphylaxis action plan 2
• Supervised oral food challenges 2
• Prevention of unnecessary dietary restrictions 2