What is a comprehensive blood allergy panel to test for common allergens?

Blood Allergy Panel for Common Allergens

For a comprehensive blood allergy panel testing common allergens, order serum specific IgE testing for the major food allergens (cow's milk, eggs, wheat, soy, peanut, tree nuts, fish, shellfish) and common environmental allergens (dust mites, pollens, molds, animal dander) using a fluorescence-labeled immunoassay platform like ImmunoCAP. 1

Selecting Allergens Based on Clinical Context

The allergen panel should be tailored to the patient's age, symptoms, and suspected exposures rather than ordering indiscriminate screening panels 1:

For Food Allergens

• Pediatric patients (especially under 5 years): Test for cow's milk, eggs, wheat, soy, and peanut, which are the most common food allergens in this age group 1
• All ages with suspected food allergy: Include tree nuts, fish, and shellfish based on dietary history and symptom timing 2, 1
• The clinical history should identify symptoms occurring within minutes to 2 hours after food ingestion, especially if reproducible on multiple occasions 3

For Environmental Allergens

• Inhalant allergens: Test for dust mites, common pollens (tree, grass, weed based on geography), molds, and animal dander (cat, dog) 2, 1
• Selection should be based on geographic location, seasonal patterns of symptoms, and environmental exposures 1

Recommended Testing Platform

Use fluorescence-labeled antibody assays such as ImmunoCAP rather than outdated RAST testing 3, 1:

• These modern platforms provide standardized, quantitative results with established predictive values 3
• Results from different laboratory platforms are not interchangeable, so predictive values established for one system cannot be applied to another 4, 1

When Blood Testing is Preferred Over Skin Testing

Serum specific IgE testing should be ordered instead of skin prick testing in these situations 1:

• Extensive dermatitis or dermatographism that prevents reliable skin testing (sensitivity 70-75% compared to skin testing) 1
• Inability to discontinue antihistamines, as serum IgE is unaffected by antihistamines unlike skin tests 1
• Uncooperative patients or very young children where blood draw is more practical 1

Critical Interpretation Guidelines

Understanding Test Limitations

The most important pitfall to avoid is equating a positive test result with clinical allergy 2, 1:

• **Negative result (<0.35 kU/L)**: Effectively rules out IgE-mediated allergy with >95% negative predictive value 3, 1
• Positive result (≥0.35 kU/L): Indicates sensitization only, NOT necessarily clinical allergy, and requires correlation with clinical history 3, 1
• The positive predictive value is only 40-60%, meaning many positive tests occur in patients who tolerate the food 1

Common Diagnostic Errors

• Do not diagnose allergy based solely on positive serum IgE without clinical correlation—this leads to unnecessary dietary restrictions 2, 1
• Do not order testing without clear clinical indication—testing should confirm suspected allergens based on history, not screen randomly 1
• In one study, 93% of children avoiding foods based on positive test results alone were actually tolerant when challenged 2

Diagnostic Algorithm

1. Start with detailed clinical history looking for allergic symptoms (urticaria, angioedema, respiratory symptoms, gastrointestinal symptoms) occurring proximate to allergen exposure 2

2. Order serum specific IgE testing for allergens identified as suspects from the history, using a validated fluorescence-labeled assay system 3, 1

3. Interpret results in clinical context:

   • Negative result (<0.35 kU/L) effectively rules out IgE-mediated allergy 3
   • Positive result requires correlation with clinical history and may need oral food challenge for confirmation 2, 1

4. Consider oral food challenge as the gold standard when test results and clinical history are discordant, or when positive tests need confirmation before implementing dietary restrictions 2, 1

Special Considerations

Non-IgE-Mediated Allergies

• Approximately 23.6% of children with food allergy have non-IgE-mediated disease (positive oral challenge with sIgE <0.35 kU/L) 3
• Diagnosis relies on clinical history, elimination diet, and supervised reintroduction rather than laboratory testing 3
• Conditions like food protein-induced enterocolitis syndrome and allergic colitis occur without IgE antibodies 2

Component-Resolved Diagnostics

• Component testing (e.g., Ara h 2 for peanut, ovomucoid for egg) may improve diagnostic accuracy but is not ready to replace standard testing 5, 6
• These tests can help distinguish true allergy from cross-reactivity but are not as sensitive and not widely available 5

Screening Panels

• Commercial mixture panels for common airborne allergens have moderate to high sensitivity (70.8%) and specificity (90.7%) 2, 7
• These can improve speed and reduce cost when many allergens need testing, but individual allergen testing based on clinical history is preferred 2, 1