Skin testing is one of the most useful ways to determine specific allergen sensitivity. Tests for allergen-specific immunoglobulin E (IgE) are necessary to advise patients about allergen avoidance techniques and for planning allergen immunotherapy regimens. Skin testing for antigens to which the patient is exposed is recommended over standard panel testing. Skin tests have a fairly high false-positive rate but a very good negative predictive value. A positive result is nonspecific, but a negative test result generally rules out the allergen as an asthma trigger.
If generalized dermatologic disease is present or if antihistamine or tricyclic antidepressant use cannot be suspended (as they interfere with results), or if skin testing is contraindicated, blood tests for allergen-specific IgE, such as the radioallergosorbent test (RAST), may be used instead. However, skin testing is less expensive, more sensitive, and more specific.
In patients with allergic disease, serum IgE level is elevated only approximately half the time. In most asthma patients, obtaining an IgE level is not indicated. However, levels greater than 1000 ng/mL (1 IU = 2.4 ng) may suggest another diagnosis (eg, allergic bronchopulmonary aspergillosis). Conditions such as atopic dermatitis may also result in high IgE levels.
While sputum and serum eosinophilia tests are not typically required or performed for diagnosis, some clinicians use these values to guide therapy.
Allergen-inhalation challenges are generally not needed or recommended. They require an available allergen solution and specialized centers capable of managing significant reactions.
Learn more about the workup for allergic and environmental asthma.
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Cite this: Zab Mosenifar. Fast Five Quiz: How Much Do You Know About Allergic Asthma? - Medscape - Feb 09, 2022.