PURPOSE OF THE STUDY.
The purpose of this study was to assess the performance of the basophil activation test in comparison with in vitro and in vivo assays for peanut-specific immunoglobulin (Ig)E in decreasing the need for double-blind, placebo-controlled food challenges (DBPCFC) in equivocal cases.
Peanut-allergic (PA, n = 43), peanut-sensitized but tolerant (PS, n = 36), and nonsensitized and nonallergic (NA, n = 25) children were recruited from a pediatric allergy clinic.
PA was confirmed by DBPCFC, convincing recent clinical history, or peanut-specific IgE ≥15 kU/L. PS was defined as a positive peanut skin prick test (SPT) and/or peanut-specific IgE ≥0.10 kU/L. Subjects underwent SPT, peanut-specific IgE, testing for specific IgE to peanut components (Ara h 1, 2, 3, 8, and 9) and basophil activation test (BAT) with fluorescence-activated cell sorting analysis for the basophil activation markers CD63 and CD203c. The performance of BAT was compared with the tests for specific IgE.
Twelve children whose basophils did not respond to the positive control were excluded from the analysis. PA children’s basophils showed increased expression of the activation markers in a dose-dependent manner up to 100 ng/mL peanut protein after which there was a plateau in responsiveness. Basophils from PS and NA children did not express CD63 or CD203c after stimulation even with 100 ng/mL protein. Considering each test individually, BAT performed best and decreased the diagnostic need for DBPCFC by two-thirds. Testing for Ara h2–specific IgE ≥0.53 kU/L was next best, followed by SPT ≥5-mm wheal. PN-s IgE ≥5.35 kU/L was least useful for decreasing the need for DBPCFC. Combining any of the latter 3 tests was still not as effective as the BAT to decrease need for DBPCFC.
To distinguish peanut allergy from tolerance and to decrease the need for DBPCFC, BAT is superior to other in vitro and in vivo tests for peanut-specific IgE, particularly when the history and other tests are equivocal.
As common as peanut allergy is, many children are so labeled solely by presence of a positive skin test or serum specific IgE. When a child eats peanut, has a reaction consistent with mast-cell activation, and has a positive test for peanut-specific IgE, the diagnosis is easy. But what about those who didn’t react? There is a great distinction between sensitization (presence of specific IgE without clinical reaction) and allergy (sensitization and clinical reaction). In equivocal cases, the oral food challenge is needed for diagnosis. However, a feeding test is time-consuming, expensive, and not without risk. The BAT is not commercially available, but if it becomes so, it will be a great aid in diagnosis. For now, we must remain keen historians and diagnosticians when seeing children who never had a reaction with ingestion but are sensitized to peanut.
- Copyright © 2015 by the American Academy of Pediatrics