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New diagnostic procedure for fish allergy to improve patient management

Published: August 21, 2022

Many fish-allergic patients only react to specific fish species and may therefore be able to safely consume others. Food challenges are the gold standard of diagnosis to determine allergy or tolerance. However, performing food challenges with many different fish species is not feasible. Due to a lack of reliable and simple diagnostic tests to determine which species of fish could be eaten, patients are often advised to strictly avoid all fish. This common practice is due to the fact that symptoms of fish allergy can be quite severe, including life-threatening anaphylaxis.

In their recent study published in The Journal of Allergy and Clinical Immunology: In Practice, Kalic et al. provide important insights into ways to improve the management of fish-allergic patients. The researchers used a novel diagnostic approach, which uses a multiplex IgE test to measure the concentration of IgE antibodies against allergens from ten fish species simultaneously. Presence or absence of IgE to a specific fish could indicate allergy or tolerance, respectively.

The authors included subjects from six countries to address regional differences in the consumed fish species and the preparation methods. In cooperation with researchers from Austria, China, Denmark, Luxembourg, Norway and Spain, blood samples were collected from 263 patients with fish allergy. The multiplex IgE test used for this purpose proved to be an effective instrument for the differentiation between allergy-causing and tolerated fish species for the patients, as validated by statistical analysis. The researchers recommend that the multiplex IgE test should include not only the major fish allergen parvalbumin, but also extracts of various bony fish and cartilaginous fish. Potential reactions to other less commonly recognized allergens can be tested with the addition of these fish extracts.

With the aid of the implemented diagnostic procedure, between 60% (Spain) and 90% (Luxembourg) of the patients were tested negative to the parvalbumin and extracts from ray, a cartilaginous fish, indicating its potential tolerance. Remarkably, up to 38% of the patients were negative to the parvalbumin from codfish, the most commonly used molecule in fish allergy diagnosis. Up to 21% of the patients, depending on their country of origin, were negative to one or more commonly consumed bony fish species.

In order to determine how to best identify potentially tolerated species, the researchers calculated the probability of an IgE test to be negative for a specific fish species, when the test had already been negative for another species. Negativity to tuna and mackerel showed the highest likelihood of negativity not only to ray but also to other bony fish. Specifically, patients negative to tuna had a 92% probability to be also negative to ray and swordfish. If negative to mackerel, a 93% chance exists to be negative to herring and ray, and 86% to swordfish. However, if negative to salmon, the probability of IgE tests to be negative to other bony fish is less than 58%. The authors concluded that these findings should be considered when designing a panel of species for tolerance-confirming food challenges.

Kalic et al. emphasize that the multiplex IgE testing could be used as a first, but not the final step in diagnosis. If no allergy-causing IgE is detected for one or more fish species, this result will have to be confirmed by a food challenge in a controlled clinical setting. Ultimately, using multiplex IgE testing for fish-allergy diagnosis could drastically reduce the number of required food challenges and help identify tolerated fish for each patient, thereby avoiding unnecessary dietary restrictions.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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