In a child with persistent atopic dermatitis despite adequate emollient use and low‑dose topical corticosteroids, suspected food allergy, what is the most appropriate investigation?

Supervised Food Challenge is the Most Appropriate Investigation

In a child with persistent atopic dermatitis despite adequate emollient use and low-dose topical corticosteroids where food allergy is suspected, the most appropriate investigation is a supervised food challenge (Option C), but only after initial screening with skin prick testing or specific IgE levels to guide which foods to challenge. 1

Diagnostic Algorithm for Food Allergy in Persistent Atopic Dermatitis

Step 1: Optimize Topical Treatment First

Before attributing symptoms to food allergy, ensure the child is receiving appropriate-potency topical corticosteroids and adequate emollient use, as many children have inadequately treated atopic dermatitis rather than true food allergy. 1 This is a critical pitfall—often avoidance is prescribed without proper treatment of the underlying dermatitis. 1

Step 2: Establish Clinical Correlation

• Ask parents to keep a food diary for one month to establish temporal correlation between food intake and eczema flare-ups. 1
• Look for immediate reactions (within minutes to 2-3 hours) versus delayed effects (2-4 days after exposure). 1
• Food allergy is relevant in only 35% of children with moderate-to-severe atopic dermatitis, so clinical history is paramount. 1

Step 3: Initial Screening Tests

• Perform limited testing for common allergens (milk, eggs, wheat, soy, peanuts) using either skin prick testing (Option B) or specific IgE levels (Option A). 1
• These tests have high negative predictive value (>95%) but poor positive predictive value (40-60%), meaning negative results effectively rule out food allergy, but positive results only indicate sensitization, not true allergy. 1, 2
• Extensive allergy testing should not be performed without clear medical history, as positive results may only reflect sensitization rather than true allergy. 1

Step 4: Supervised Food Challenge (The Gold Standard)

• A supervised oral food challenge under allergist guidance is essential to confirm the diagnosis, as improvement during elimination may be coincidental or placebo effect. 1
• The double-blind, placebo-controlled food challenge (DBPCFC) is considered the gold standard for diagnosing food allergy. 1
• Evaluate skin status with an established score (SCORAD or EASI) at 24 hours and later after challenge. 1

Step 5: Diagnostic Elimination Diet (If Needed)

• A diagnostic elimination diet should be performed for 4-6 weeks, followed by an oral food challenge under medical supervision to confirm the diagnosis. 1
• Do not start an elimination diet based solely on the presence of atopic dermatitis or a suspected history—use a stepwise approach including initial testing and subsequent dietary elimination and challenge. 1

Why Each Option Ranks as It Does

Option C (Supervised Food Challenge) - BEST ANSWER

This is the definitive diagnostic test that confirms true food allergy versus sensitization alone. 1 However, it should be preceded by screening tests to determine which foods to challenge. 1

Option B (Prick Skin Test) - Initial Screening

Useful as a first-line screening tool with high negative predictive value, but requires confirmation with food challenge due to poor positive predictive value. 1, 2 This is the practical starting point before proceeding to supervised challenge. 1

Option A (IgE Levels) - Alternative Screening

Can be used as an alternative to skin prick testing, especially in cases with widespread skin lesions or marked dermatographism. 1 Like skin prick testing, positive results require confirmation with supervised challenge. 1, 2

Option D (Food Elimination) - AVOID Without Confirmation

Prolonged and multiple elimination diets can be harmful, leading to weight loss, growth delay, calcium deficiency, and other nutritional deficiencies. 1 Elimination should only occur after establishing clinical relevance through proper testing and challenge. 1, 3

Critical Pitfalls to Avoid

• Never prescribe avoidance without treating the underlying atopic dermatitis. 1 Effective treatment remains skin care and topical therapies, even in the presence of confirmed food allergy. 1
• Avoid broad panel allergy testing without clear clinical history, as this leads to false-positive results and unnecessary dietary restrictions. 1, 3
• Do not rely on positive IgE or skin prick tests alone—up to 93% of sensitized children actually tolerate the food. 4 Confirmation with supervised challenge is mandatory. 1
• Avoid empiric food elimination without proper testing, as this can cause nutritional deficiencies and paradoxically increase the risk of developing IgE-mediated food allergy. 5, 3

When to Refer to Allergist

Referral to an allergist is recommended for longitudinal care, diagnostic testing, formulation of emergency anaphylaxis action plan, and supervised oral food challenges. 1 The allergist will help facilitate proper elimination diets under specialist supervision and prevent unnecessary dietary restrictions. 1