Identification of Potentially Tolerated Fish Species by Multiplex IgE Testing of a Multinational Fish-Allergic Patient Cohort

Background: Although recent studies indicated that many fish-allergic patients may safely consume certain fish species, no clinical guidelines are available for identification of the exact species tolerated by specific patients. Objective: To investigate whether multiplex immunoglobulin E (IgE) testing reveals potentially tolerated fish through absence of IgE to parvalbumin (PV) and extracts from specific species. Methods: Sera from 263 clinically well-defined fish-allergic patients from Austria, China, Denmark, Luxembourg, Norway, and Spain were used in a research version of the ALEX² multiplex IgE quantification assay. Specific IgE to PVs from 10 fish species (9 bony and 1 cartilaginous), and to extracts from 7 species was quantified. The IgE signatures of individual patients and patient groups were analyzed using SPSS and R. Results: Up to 38% of the patients were negative to cod PV, the most commonly used molecule in fish allergy diagnosis. Forty-five patients (17%) tested negative to PVs but positive to the respective fish extracts, underlining the requirement for extracts for accurate diagnosis. Between 60% (Spain) and 90% (Luxembourg) of the patients were negative to PV and extracts from ray, a cartilaginous fish, indicating its potential tolerance. Up to 21% of the patients were negative to at least 1 bony fish species. Of the species analyzed, negativity to mackerel emerged as the best predictive marker of negativity to additional bony fish, such as herring and swordfish. Conclusions: Parvalbumins and extracts from multiple fish species relevant for consumption should be used in fish-allergy diagnosis, which may help identify potentially tolerated species for individual patients.