What is the best diagnostic approach for testing food allergies in children with atopic dermatitis?

Diagnostic Testing for Food Allergy in Children with Atopic Dermatitis

In children with atopic dermatitis, do not perform food allergy testing routinely—only test children under 5 years old with moderate-to-severe disease that persists despite optimized topical corticosteroid and emollient therapy, limiting initial testing to milk, eggs, wheat, soy, and peanuts. 1, 2, 3

When to Test: Specific Criteria Required

Food allergy testing is indicated only when ALL of the following are present:

• Child is under 5 years of age 1, 2
• Moderate-to-severe atopic dermatitis (not mild disease) 1, 3
• Disease persists despite optimized management, meaning adequate-potency topical corticosteroids AND regular emollient use have been properly applied 1, 2, 3
• OR a reliable history of immediate allergic reaction (urticaria, angioedema, respiratory symptoms, or anaphylaxis within 2 hours) after ingesting a specific food 1

Critical pitfall: Food allergy is relevant in only 35% of children with moderate-to-severe atopic dermatitis, and most children have inadequately treated eczema rather than food-triggered disease. 1, 2, 3

Which Tests to Use

First-Line Testing Options

Skin prick testing (SPT) or food-specific IgE blood testing are the recommended initial tests: 1

• SPT advantages: Rapid results (15-20 minutes), high negative predictive value (>95%), preferred unless extensive skin lesions, marked dermatographism, or recent antihistamine use 1
• Specific IgE testing advantages: Useful when SPT cannot be performed due to widespread eczema or dermatographism 1, 3
• Both tests have poor positive predictive value (40-60%), meaning positive results only indicate sensitization, NOT confirmed allergy 1, 3, 1

Which Foods to Test Initially

Limit testing to the "critical five" allergens: cow's milk, eggs, wheat, soy, and peanuts in children under 5 years 1, 2, 3

In older children, if testing is warranted based on history, also consider tree nuts, fish, and shellfish. 1

Tests NOT Recommended

• Total serum IgE levels: Not helpful for diagnosing food allergy 1
• Intradermal testing: Not recommended 1
• Atopy patch testing (APT): Not routinely used in North America, though studied in Europe 1
• Broad panel allergy testing without clinical history: Leads to false-positive results and harmful dietary restrictions 2, 3

Confirming the Diagnosis: The Essential Next Steps

Positive SPT or specific IgE results alone are NOT sufficient for diagnosis—they only demonstrate sensitization. 1, 3 The following stepwise approach is mandatory:

Step 1: Diagnostic Elimination Diet

• Remove the suspected food for 4-6 weeks while maintaining optimal topical therapy 1, 2, 3
• Monitor for improvement using objective scoring (SCORAD or EASI) 2
• Keep a detailed food diary to document any correlation between food exposure and symptom flares 1

Step 2: Oral Food Challenge (Gold Standard)

An oral food challenge under allergist supervision is essential to confirm diagnosis, as improvement during elimination may be coincidental or placebo effect. 2, 3, 1

• Double-blind, placebo-controlled food challenge (DBPCFC) is the international gold standard 1, 3
• Open-label challenges are acceptable in clinical practice 3
• Challenges must be performed in a medically supervised setting due to risk of severe reactions 1, 4

Without oral food challenge confirmation, you cannot definitively diagnose food-triggered atopic dermatitis. 4, 5

When to Refer to an Allergist

Refer to an allergist for: 1, 2

• Supervised oral food challenges to confirm or exclude food allergy 1, 2
• Formulation of emergency anaphylaxis action plans and epinephrine autoinjector prescription 1
• Longitudinal care and regular re-evaluation for development of tolerance 1, 2
• Prevention of unnecessary dietary restrictions that can cause nutritional deficiencies 2, 3

Critical Pitfalls to Avoid

Pitfall 1: Testing Without Optimizing Topical Therapy First

Most children have inadequately treated atopic dermatitis, not food allergy. 2, 3 Before attributing symptoms to food:

• Ensure appropriate-potency topical corticosteroids are being used correctly 1, 2
• Confirm regular emollient application to maintain skin barrier 2, 6
• Treat the underlying eczema aggressively first 1

Pitfall 2: Implementing Elimination Diets Based on Positive Tests Alone

50-90% of presumed food allergies based on symptoms or positive tests are not true allergies. 3 Eliminating foods without oral challenge confirmation leads to:

• Weight loss and growth delay 2, 3
• Calcium deficiency and hypovitaminosis 2, 3
• Kwashiorkor in severe cases 2
• Unnecessary dietary restrictions that impair quality of life 1, 3

Pitfall 3: Forgetting That Effective Treatment Remains Topical Therapy

Even with confirmed food allergy, the primary treatment of atopic dermatitis remains skin care and topical corticosteroids. 2, 3 Often avoidance is prescribed while the underlying eczema goes untreated, which is incorrect management. 1, 2

Understanding Test Interpretation

Negative Test Results

• High negative predictive value (>95%) effectively rules out IgE-mediated food allergy 1
• No further testing or elimination needed for that food 1

Positive Test Results

• Only indicate sensitization, not clinical allergy 1, 3
• Larger wheal sizes (>8-10 mm) or higher specific IgE levels increase likelihood of true allergy but still require confirmation 1
• Component-resolved diagnostics (measuring IgE to specific food proteins like Ara h 2 for peanuts) may improve specificity in borderline cases 1

Special Considerations

Immediate vs. Delayed Reactions

Food can trigger two distinct reaction types in atopic dermatitis patients: 1, 2

• Immediate/Type I reactions (within 2 hours): urticaria, angioedema, respiratory symptoms, anaphylaxis—these are IgE-mediated and detected by SPT/specific IgE 1
• Delayed eczematous reactions (6-48 hours later): worsening of dermatitis—these are harder to diagnose and require elimination diet plus oral challenge 1, 2

Most food reactions in atopic dermatitis are immediate-type, not eczematous flares. 4

Age-Related Considerations

• Infants and young children: Milk, eggs, soy, wheat, peanuts most common 7
• Older children: Tree nuts, fish, shellfish become more relevant 1, 7
• Adolescents/adults: Consider pollen-related food allergy (oral allergy syndrome)—birch pollen allergic patients may react to apples, celery, carrots, hazelnuts 1

Natural History and Re-evaluation

Most children with food allergies develop tolerance over time, requiring regular re-evaluation. 2 Annual follow-up with repeat testing and potential oral challenges is recommended to avoid prolonged unnecessary dietary restrictions. 1