Accurate diagnosis of food allergy is essential for personalised patient management,1 including avoidance of unnecessary dietary restrictions and prevention of life-threatening reactions.2 Egg is one of the most common food allergy sources, particularly in infants and children.1 The prevalence of egg allergy in children is estimated to be around 0.5-2.5 percent.3
Read through this evidence-based guide to learn how to accurately diagnose egg allergy in clinical practice.
A detailed clinical history is crucial but not sufficient alone to make a diagnosis of egg allergy. The goals of the clinical history are to:4,5
Egg allergy is most commonly IgE-mediated, and usually presents as an immediate-type reaction (within minutes to hours after ingestion).
IgE-mediated egg allergy:6
*Anaphylaxis or shock-like symptoms are clear indications for a referral to an allergy specialist.
The physical examination should thoroughly assess nutritional status and growth, especially in children, as well as associated atopic diseases such as atopic dermatitis and asthma.5
Gastroenteropathies, such as allergic eosinophilic oesophagitis, are occasionally seen in children with egg allergy, and are mediated by a combination of IgE and non-IgE immunological processes.6
If the patient’s history indicates IgE-mediated allergy, specific IgE blood tests can assist in the diagnosis.7,8 Specific IgE blood tests can be performed at any age and use validated assays to quantify allergen-specific IgE levels in the serum.7 Firstly, a test for a specific IgE response to the whole allergen (egg) should be performed.8
Interpretation of whole-allergen specific IgE blood test results
Whole-allergen tests predict the likelihood of egg allergy but are not predictive of reactivity to cooked egg. After testing for a specific IgE response to whole allergen, egg allergen component tests can help evaluate reactivity to cooked egg and provide further information on the likelihood of allergy persistence.6,8
Assessment of specific IgE responses to the following components (proteins) could help pinpoint the diagnosis and guide the management of patients with egg allergy:8
As ovomucoid is more resistant than other proteins to heat denaturation, patients with high levels of ovomucoid-specific IgE are likely to react to cooked egg. Such patients should therefore avoid consumption of all forms of egg. Patients who test negative for ovomucoid-specific IgE may be able to tolerate cooked egg.8
If relevant symptoms are present and egg allergy is likely, a diagnostic elimination diet should be initiated. Egg should be strictly excluded from the patient’s diet for a limited period.5
The duration of the elimination diet should be kept as short as possible whilst being long enough to judge whether clinical symptoms resolve or stabilise (usually 2-4 weeks for IgE-mediated symptoms). Symptoms should be carefully monitored:5
Sometimes the clinical history and specific IgE blood test results are strongly suggestive of an egg allergy, but often an OFC with egg is necessary to confirm the diagnosis. The presence or absence of a symptomatic response will demonstrate allergy or tolerance, respectively.5
OFCs should be performed in a specialist setting with rapid emergency support available; for patients deemed by their healthcare provider to be at medium-to-high risk of having a severe reaction, intensive care support must also be immediately available.5
When a diagnosis of egg allergy has been confirmed, avoidance of egg-containing food should form the basis of the management strategy.11 As egg is found in a wide range of food products, dietary avoidance can be challenging and pose significant quality-of-life concerns.6 Elimination diets in young children may result in poor nutrition, meaning growth parameters should be closely monitored.11
Based on allergen-component blood test results, patients may be able to tolerate extensively heated egg.11 Dietary inclusion of products containing extensively heated egg may accelerate development of tolerance to unheated egg.6
Patients should be re-evaluated at around 6-12 months, to avoid continuing the restrictive exclusion diet for an unnecessarily long time. Repeated specific IgE blood tests can be helpful to:5
IgE: immunoglobulin E
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