Recommended Initial Test for IgE-Specific Testing
Skin prick testing should be used as the initial test for patients requiring IgE-specific testing due to its superior sensitivity, specificity, and rapid results compared to in vitro blood tests. 1, 2
Rationale for Skin Testing as First-Line
Skin testing offers several advantages as the initial diagnostic approach:
- Superior sensitivity and specificity: Skin prick tests demonstrate >80% sensitivity and specificity for detecting allergen-specific IgE 1
- Immediate results: Results are available within 15-20 minutes 1
- Cost-effectiveness: Simpler, less expensive, and more rapid than in vitro testing 1
- Historical precedent: Has been the primary diagnostic tool in clinical studies of allergen immunotherapy 1
According to the American Academy of Allergy, Asthma, and Immunology practice parameter, "skin testing has been the primary diagnostic tool in clinical studies of allergen immunotherapy. Therefore in most patients, skin testing should be used to determine whether the patient has specific IgE antibodies." 1
Proper Skin Testing Technique
For optimal results, skin testing should follow these guidelines:
- Begin with percutaneous (prick/puncture) testing, which produces reproducible results 1
- Use standardized allergen extracts when available 1
- Include appropriate positive and negative controls 1
- Record measurements of wheal and erythema at 15-20 minutes after placement 1
- Document all medications taken within the past week that might suppress skin test response 1
When to Consider In Vitro Testing Instead
While skin testing is preferred, in vitro specific IgE testing is appropriate in certain situations:
- Extensive skin disease (e.g., dermatographism, atopic dermatitis) 1, 2
- Patients taking medications that suppress skin test reactions (e.g., antihistamines) that cannot be discontinued 1, 2
- Uncooperative patients 1
- History suggesting high risk of anaphylaxis from skin testing 1
Limitations of In Vitro Testing
When using in vitro testing, be aware of these limitations:
- Lower sensitivity compared to skin testing (70-75% on average) 1, 2
- Results can vary between different laboratory systems 2
- Total serum IgE has limited diagnostic value and should not be used alone for allergy diagnosis 2
Clinical Correlation is Essential
Regardless of testing method:
- Positive test results must be correlated with clinical history and physical findings 1, 2
- The presence of specific IgE without clinical symptoms is not sufficient for diagnosis 2, 3
- Higher levels of specific IgE may correlate with higher probability of clinical reactivity, but this varies by allergen and patient population 2
Important Caveats
- Negative skin test results with positive in vitro results may warrant further investigation, especially for Hymenoptera venom allergy 1
- Testing should be based on clinical history of relevant symptoms with knowledge of possible environmental exposures 1
- The number of skin tests and allergens selected should be determined based on patient's age, history, environment, and living situation 1
By following this evidence-based approach to IgE-specific testing, clinicians can optimize diagnostic accuracy while minimizing unnecessary testing and patient discomfort.