From the Guidelines
Requesting a total IgE level before proceeding to specific allergen testing like RAST is not a correct diagnostic approach for IgE-mediated food allergies. Total IgE levels have poor predictive value for food allergies as they can be elevated in many conditions unrelated to food allergies, such as parasitic infections, atopic dermatitis, and asthma 1. Conversely, patients with genuine food allergies may have normal total IgE levels.
Key Points to Consider
- The recommended approach is to proceed directly to allergen-specific IgE testing (like RAST or ImmunoCAP) based on the patient's clinical history of reactions to specific foods 1.
- These tests measure IgE antibodies to specific food allergens rather than total IgE, providing more clinically relevant information.
- However, even specific IgE testing should be interpreted cautiously, as positive results indicate sensitization but not necessarily clinical allergy.
- The gold standard for diagnosing food allergies remains a combination of clinical history, specific IgE testing, and, when appropriate, oral food challenges under medical supervision.
Diagnostic Approach
- A thorough medical history is essential in identifying symptoms associated with food allergies and focusing the diagnostic workup 1.
- Physical examination may provide signs consistent with an allergic reaction or disorder often associated with food allergies, but it cannot be considered diagnostic of food allergy on its own 1.
- Allergen-specific serum IgE tests, such as RAST or ImmunoCAP, are useful for identifying foods that potentially provoke IgE-mediated food-induced allergic reactions, but alone these tests are not diagnostic of food allergy 1.
From the Research
Diagnosis Approach for Food Allergy
- The approach of requesting a total Immunoglobulin E (IgE) level before proceeding to a RadioAllergoSorbent test (RAST) is not entirely incorrect, but it may not be the most efficient or recommended method for diagnosing IgE-mediated food allergy 2, 3.
- A firm diagnosis of food allergy is crucial to avoid misdiagnosis, which could lead to life-threatening reactions or unnecessary elimination diets with nutritional and social implications 2.
- Simple tests, including skin-prick testing (SPT) and serum food-specific IgE testing, are commonly used to evaluate for IgE-mediated food reactions, but they have pitfalls and their usefulness must be appreciated to avoid over- and underdiagnosis 2, 3.
- A careful medical history and simple tests can often provide a reliable diagnosis, and physician-supervised oral food challenges (OFC) remain the gold standard for food allergy diagnosis 2, 3.
Diagnostic Tests for Food Allergy
- Skin-prick testing (SPT) and serum food-specific IgE testing are the most commonly used diagnostic tests to evaluate for IgE-mediated food reactions 2, 3.
- Component-resolved diagnostics, atopy patch testing, and the basophil activation test are emerging tests that may be of benefit in the future 2, 3.
- The choice of food allergy testing modality should be informed by the reaction history and determined by the testing goals 4.
Importance of Medical History
- A food reaction history is the basis of food allergy diagnoses, and a careful medical history paired with SPT and serum food-specific IgE testing can often provide a reliable diagnosis 2, 3, 4.
- The goal of food allergy testing may be merely to confirm the diagnosis of food allergy or may be used to guide passive (avoidance) or active (allergen immunotherapy) management 4.