Unreliable allergy testing puts lives at risk

Commercial fish extracts are often used in skin-prick testing (SPT) for diagnosing fish allergy—but they are insufficient for reliable testing and may be jeopardizing lives, according to the results of a recent Australian study published in Allergy.

“We urgently need reliable tools to diagnose fish allergy, a serious and often life-threatening immune disease. Current tests can be falsely negative, putting lives at risk,” said lead author and PhD candidate Thimo Ruethers, Australian Institute for Tropical Health and Medicine (AITHM), and Molecular Allergy Research Laboratory, College of Public Health, Medical, and Veterinary Sciences, James Cook University (JCU), Townsville, Queensland, Australia.

Fish allergy is serious business, affecting up to 3% of the general population and up to 8% of fish-processing workers. Although rare, this food allergy can result in life-threatening anaphylaxis.

Over 1,000 species of fish are consumed globally. However, only 30 commercial fish extracts (largely European species) are available for SPT, which may leave some allergen-sensitive populations vulnerable. This gap in available fish extracts, coupled with the lack of regulatory standardization of protein and allergen content, has called into question the integrity of SPT results.

“There are no regulations requiring the standardization of commercial preparations for skin-prick testing, while improved preparations are pricey and often impossible to get,” said senior author Andreas L. Lopata, PhD, professor, AITHM, and Molecular Allergy Research Laboratory, College of Public Health, Medical, and Veterinary Sciences, JCU.

For this study, the researchers assessed protein and allergen concentrations from commercial fish extracts using serum from fish-allergic patients. Specifically, they examined 26 commercial SPT fish extracts from five different manufacturers—representing 11 fish families or groups, including mixed species. Biochemical and immunological analysis of complete protein and allergen content was determined via immunoblotting and advanced mass spectrometric analysis.

The investigators aimed to be as robust as possible in their analysis, and sought out allergens including parvalbumin, tropomyosin, aldolase, and collagen. They also examined molecular IgE reactivity using serum from 16 fish-allergic children hailing from the Southern hemisphere. These children were mostly allergic to cod, tuna, and salmon.

In all, high variability in the protein and allergen content appeared to plague fish SPT extracts, thus floundering their accuracy.

“We found the amount of allergens present varied greatly, and in some preparations major fish allergens could not be detected. This means many skin prick tests that show a person being tested is not allergic to fish may be wrong,” said Ruethers.

Total protein concentrations among the 26 fish extracts varied by up to 17-fold, from the lowest in flounder-2 (0.17 mg/mL) to the highest in tuna-1 (2.94 mg/mL). Parvalbumin, a major fish allergen, was not detected by immunoblotting in 6 of 26 extracts. Five known fish allergens were detected by mass spectrometry in 7 of 12 extracts.

With respect to cod and tuna, nearly 70% of patients exhibited the strongest IgE reactivity to collagen, tropomyosin, aldolase A, or β-enolase, but not parvalbumin. Although parvalbumin accounts for 70% to 95% of allergic fish reactions, 9 of 16 fish-allergic study participants also demonstrated strong reactivity to collagen, suggesting the importance of additional fish allergens among the various fish species.

“Many commercial fish extracts contain insufficient amounts of allergens such as parvalbumin and collagen, resulting in low IgE reactivity and limited suitability for reliable in vivo allergy testing,” concluded the authors. “We recommend either standardization and regulation of protein concentration and profiles in commercial allergen extracts or the use of improved in vitro diagnostics implementing a large variety of fish species and purified allergens.”