What blood tests are recommended for diagnosing a mild egg allergy?

Blood Testing for Mild Egg Allergy

For suspected mild egg allergy, order egg white-specific IgE testing, which serves as the primary blood test to identify IgE-mediated sensitization, though this alone cannot diagnose clinical allergy without correlation to clinical history. 1

Recommended Blood Test

• Egg white-specific IgE (sIgE) is the standard blood test for evaluating suspected egg allergy 1
• The test should use modern fluorescence-labeled antibody assays (such as ImmunoCAP), not the outdated RAST terminology 1
• Specific IgE testing is particularly useful when skin prick testing cannot be performed due to extensive dermatitis, dermatographism, or inability to discontinue antihistamines 1

Interpreting Results

• A negative sIgE result (<0.35 kUA/L) has high negative predictive value (>95%) and effectively rules out IgE-mediated egg allergy 1, 2
• A positive sIgE result indicates sensitization only, not necessarily clinical allergy - it must be correlated with clinical history 1, 2
• Higher sIgE levels correlate with increased probability of clinical reactivity, though predictive values vary between studies 1
• Some evidence suggests higher IgE levels may correlate with more severe reactions 3

Component-Resolved Diagnostics (Advanced Testing)

• Ovomucoid-specific IgE (Gal d 1) can provide additional diagnostic information and may predict persistent allergy and reactivity to heated egg 1, 4
• Other egg components include Gal d 2,3, and 5, though these are primarily available in specialized centers 1
• Component testing is not routinely necessary for initial diagnosis but may help distinguish clinical phenotypes 1, 4

Tests NOT Recommended

• Total serum IgE should NOT be measured for diagnosing egg allergy, as it lacks sufficient sensitivity and specificity 1
• The ratio of specific IgE to total IgE offers no diagnostic advantage 1
• Food allergen panel testing should be avoided due to poor positive predictive value leading to over-diagnosis 1

Critical Diagnostic Algorithm

1. Start with clinical history - symptoms occurring within minutes to hours after egg ingestion, especially if reproducible on multiple occasions 1, 2
2. Order egg white-specific IgE as the blood test of choice 1
3. Interpret results in clinical context - positive tests require clinical correlation; negative tests effectively rule out IgE-mediated allergy 2
4. Consider oral food challenge if diagnosis remains uncertain, as this remains the gold standard 1, 2

Important Caveats

• Different laboratory assay systems (ImmunoCAP, Turbo-MP, Immulite) provide significantly different measurements for the same serum samples, so predictive values from one system cannot be applied to another 1
• Positive blood tests only indicate sensitization; 50-90% of presumed food allergies based on history alone are not actual allergies when formally tested 2
• Most children with egg allergy develop tolerance over time, so retesting is warranted as the child ages 1