The mere detection of sensitization to an allergen on allergen-specific immunoglobulin E (IgE) tests is not always equivalent to a clinical diagnosis, cautioned a clinical report from the American Academy of Pediatrics (AAP).
As a result, "patients should not be told they are allergic based solely on either a skin test or the identification of [allergen-specific immunoglobulin]," wrote Scott Sicherer, MD, and colleagues from the AAP section on allergy and immunology.
Most allergies result in the production of IgE antibodies that are specific to that allergen. The report, published in the January 2012 issue of Pediatrics, offers aid to pediatricians in selecting the appropriate allergy tests, and interpreting the results in the context of a patient history and clinical presentation.
In-vitro allergen-specific immunoglobulin E (sIgE) testing is widely available to physicians, but the report sets out several caveats that physicians need to keep in mind when using these tests and before embarking on immunotherapy.
First and foremost, the limits of IgE tests highlight the importance of obtaining a detailed medical history and tests must be interpreted in the presence of a clinical presentation, the authors noted.
For instance, a child who eats eggs without any symptoms does not need to undergo testing for an egg allergy. The same holds true for pollen testing when a child is not physically exposed to a certain pollen.
"Testing large panels of allergens without consideration of history, geographic relevance, and disease characteristics may result in many clinically irrelevant positive results," the authors warned.
Overall, the enzymatic assays available for allergen-specific testing offer "excellent" performance, but individual systems appear to detect different populations of IgE antibodies, the authors stated. Pediatricians need to be aware that results for allergens may differ between the testing systems.
Both serum sIgE tests and skin-prick tests have similar diagnostic properties with specific pros and cons. Skin-prick tests offer immediate results and are low cost, but they require the availability of rash-free skin.
Serologic tests aren't affected by antihistamines or extensive dermatitis, but require a blood sample and cost more.
The report also includes guidance on specific allergies:
- Asthma: Follow national guidelines and test for indoor allergens (dust mites, mold)
- Food: There is no current evidence that testing for total IgE will identify specific food allergies
- Drugs: IgE tests are not relevant for many drug reactions
- Latex: The diagnostic value of serum tests is not well characterized
- Insect venom: A localized reaction at the bite or sting site does not indicate a risk for anaphylaxis; testing is not warranted
Finally, the report recommended that pediatricians consult with an allergist-immunologist to confirm the role of specific allergens in patient allergies and to guide immunotherapy.
AAP clinical reports expire five years after publication unless reaffirmed, amended, or retired at five years or before.
Any author conflicts have been resolved by the AAP board of directors.