Why does a patient with a positive test result for Immunoglobulin A (IgA) and Immunoglobulin G (IgG) antibodies to egg whites experience worsened symptoms when consuming eggs with slightly runny egg whites?

Why Runny Egg Whites Cause Worse Symptoms in Egg-Allergic Patients

The patient experiences worse symptoms with runny egg whites because heat-labile egg proteins—particularly ovomucoid, ovalbumin, and ovotransferrin—retain their full allergenic structure when undercooked, whereas thorough heating denatures these proteins and significantly reduces their allergenicity. 1

The Science Behind Heat and Egg Allergenicity

Protein Structure and Allergenicity

The key egg white allergens include ovomucoid (Gal d1), ovalbumin (Gal d2), ovotransferrin (Gal d3), and lysozyme (Gal d4). 2 Among these proteins, ovomucoid plays the most critical role in allergic reactions, particularly to heated egg products. 1

Research demonstrates that:

• Ovomucoid is heat-stable, meaning it retains significant allergenicity even after cooking 1
• Ovalbumin and ovotransferrin are heat-labile, meaning their allergenic structure breaks down substantially with adequate heating 1
• Patients who react to heated eggs have significantly higher IgE antibody levels to ovomucoid compared to those who tolerate heated eggs 1

Clinical Evidence of Heat's Protective Effect

A pivotal study using double-blind, placebo-controlled food challenges revealed that:

• 21 of 38 patients (55%) who reacted to freeze-dried (raw) egg white had negative reactions to heated egg white 1
• Patients with positive reactions to heated egg white had significantly higher ovomucoid-specific IgE levels 1
• When ovomucoid was depleted from heated egg white, 16 of 17 patients (94%) who previously reacted to heated egg white no longer had reactions 1

Why Runny Eggs Are More Problematic

When egg whites remain runny or undercooked:

• All allergenic proteins maintain their native three-dimensional structure, maximizing IgE antibody binding sites 3, 1
• The heat-labile proteins (ovalbumin, ovotransferrin) remain fully allergenic 1
• Even the heat-stable ovomucoid retains maximum allergenicity 1

In contrast, thoroughly cooked eggs undergo protein denaturation that:

• Disrupts the conformational epitopes (3D structure-dependent binding sites) 1
• Reduces overall IgE-binding capacity 3
• Makes eggs tolerable for approximately 55% of egg-allergic patients 1

Clinical Implications for This Patient

Understanding the IgA and IgG Results

Important caveat: The patient's positive IgA and IgG tests to egg whites are not diagnostic of clinical egg allergy. 4

• IgG antibodies are exposure-dependent markers, not indicators of true food intolerance or allergy 4
• IgG testing has "poor specificity and applicability" for identifying problematic foods, with 87% of patients testing positive to foods they actually tolerate 4
• True egg allergy is IgE-mediated, not IgA or IgG-mediated 5

What Testing Should Be Done

If this patient has genuine allergic symptoms to eggs, the appropriate diagnostic approach includes:

• Serum-specific IgE testing to egg white, ovomucoid, ovalbumin, and ovotransferrin 5
• Skin prick testing (SPT) with egg white extracts 5
• Correlation of test results with clinical history of reactions 5
• Potentially an oral food challenge under allergist supervision if diagnosis remains unclear 5

Management Recommendations

For patients with confirmed IgE-mediated egg allergy experiencing worse symptoms with runny eggs:

1. Advise complete avoidance of raw and undercooked eggs 5
2. Consider evaluation for tolerance to extensively heated egg products (baked goods containing egg) under allergist supervision 5, 1
3. Prescribe epinephrine autoinjectors if there is any history of systemic reactions, respiratory symptoms, or anaphylaxis 5
4. Prescribe antihistamines for mild, isolated skin reactions 5
5. Refer to an allergist for comprehensive evaluation, particularly if the patient has moderate-to-severe atopic dermatitis or multiple food allergies 5

Common Pitfall to Avoid

Do not restrict the diet based solely on IgA/IgG testing results. 4 Multiple gastroenterology societies recommend against using IgG antibody testing for food elimination decisions due to poor specificity and limited evidence. 4 The British Society of Gastroenterology states that IgG-guided elimination diets are "not recommended." 4

If this patient tolerates well-cooked eggs without symptoms, the positive IgA/IgG tests likely represent sensitization without clinical allergy, and unnecessary dietary restrictions could lead to nutritional deficiencies. 5