Overview of suggested approach to testing in a patient with a convincing or suggestive history of IgE-mediated food allergy*

IgE: immunoglobulin E; SPT: skin prick test.
* Several factors determine whether a history is consistent with an IgE-mediated reaction, including the signs and symptoms of the reaction (common findings include urticaria, nausea/vomiting, wheezing), timing in relation to food ingestion (usually within minutes), and the food trigger suspected (eg, a common allergen such as peanut or an uncommon allergen such as grape). If all factors are consistent with an IgE-mediated reaction, the pretest probability is very high. If some are present, the pretest probability is intermediate. If most to all of the factors are absent, then an IgE-mediated reaction is unlikely (low pretest probability), and testing is usually not performed.
¶ The choice of testing depends upon a several factors including availability of testing, patient/caregiver and clinician preferences, and technical limitations and accuracy of the tests. Options include SPT with food extracts or fresh foods, immunoassays to whole foods, and component immunoassays to specific food proteins. Refer to UpToDate topic on diagnosis of IgE-mediated food allergies for additional details.
Δ What constitutes a positive test varies depending upon several factors including the food, type of test, and age of the patient. For SPT, it is based upon the size of the wheal, and, for immunoassay, it depends upon the specific food being tested, the level of IgE antibody, and the assay used. Refer to UpToDate topic on diagnosis of IgE-mediated food allergies for additional details.