D3.38 - Elucidating the Causes of Discordant Results Between Two Specific IgE Assays Using Component-Resolved Diagnostics and Depletion Testing

Specific IgE testing is central to food allergy diagnosis, however, discordant qualitative results between different assay platforms frequently complicate clinical interpretation, and the underlying causes of such discordance remain poorly understood. To address this unmet diagnostic challenge, we compared two widely used in‑vitro IgE assays—DropScreen ST‑1 (Nippon Chemiphar, DS), a multiplex chemiluminescent enzyme immunoassay, and ImmunoCAP (Thermo Fisher Diagnostics, IC), a single-plex fluorescence enzyme immunoassay—for major pediatric food allergens. We then applied component-resolved diagnostics across egg, milk, and fruit allergens, and further performed allergen depletion testing for fruit allergens often implicated in pollen–food allergy syndrome (PFAS) to elucidate the mechanisms underlying assay discordance.

Serum samples from 94 patients diagnosed with egg white, milk, or fruit (peach, kiwi, apple, banana) allergy were analyzed using DS and IC. Positive rates and qualitative agreement were assessed for each allergen. For discordant cases, allergen components were measured to characterize sensitization profiles: Gal d 1–4 (egg), Bos d 4–6/8 (milk) and Bet v 1 / Bet v 2 (fruits). In fruit-allergic patients with IC-positive/DS-negative results and component patterns suggestive of PR‑10 or profilin sensitization, depletion tests using Bet v 1 and/or Bet v 2 were performed.

Positive agreement between DS and IC was high for egg white (88.4%) and milk (97.1%), indicating comparable diagnostic performance. In contrast, fruit allergens showed lower concordance, with 13 IC‑positive/DS‑negative cases. Component testing was available for 11 of these cases, of which 6 demonstrated sensitization to Bet v 1 and/or Bet v 2. Depletion assays confirmed cross‑reactive sensitization, as fruit-specific IgE levels were markedly reduced after depletion with Bet v 1 and Bet v 2, supporting PR-10– and profilin-related IgE cross-reactivity.

DS and IC showed comparable qualitative performance for egg white and milk allergens. For fruit allergens, discordant IC‑positive/DS‑negative cases were largely attributable to PR‑10 and profilin sensitization, as demonstrated by CRD and depletion test. These findings suggest that IC may be more suitable for detecting sensitization to fruit allergens, while component-based analyses provide critical insight for interpreting assay discordance and evaluating fruit allergy and PFAS.