A new study has found that the contents of commercially produced extracts used to test for shellfish allergies differ widely between manufacturers. The researchers are calling for the standardization of these extracts to avoid false negative results and safeguard the health of allergy sufferers worldwide.
Shellfish allergies are the most common food allergy in adults and one of the most common in children. Worldwide, shellfish allergies affect up to 3% of the population but are particularly prevalent in Asian countries where a lot of shellfish is consumed. Shellfish allergies typically last a lifetime and can trigger anaphylaxis, a severe, potentially fatal allergic reaction.
Most people who are allergic to one type of shellfish – be it shrimp, lobster, crab, or oysters – have an allergy to other species. Skin prick testing (SPT) is the preferred method for determining food allergy. It’s safe for most patients, including babies, and results are available quickly.
But a new study led by researchers from James Cook University’s Australian Institute of Tropical Health and Medicine (AITHM) and the university’s Singapore-based Tropical Futures Institute (TFI) has found that not all commercially available SPTs for shellfish allergy are created equal.
“Skin prick testing (SPT) is often the preferred first-line diagnostic approach,” said Dianne Campbell, one of the study’s co-authors. “This involves a health worker placing a drop of allergen extract on the surface of the arm then pricking through it into the arm. If you are allergic to the allergen, you will have a small, itchy swelling and a reddening of the skin after 10-15 minutes.”
Commercially available allergen extracts are manufactured specifically for the purpose of SPT. They’re aqueous solutions of proteins extracted from the relevant allergic materials combined with glycerol, which acts as a preservative. Different manufacturer’s preparations of the same allergen may vary in their content and proportion of major allergenic proteins, due to differences in the source material, its preparation, or the techniques of allergen preparation.
In 2019, the researchers evaluated 26 commercially available fish allergen extracts used for SPT and found that the amount of allergens varied widely. In some, major fish allergens couldn’t be detected. This time, they looked at extracts used to detect shellfish allergies.
“In the current study, using biochemical and immunological methods and mass spectrometry, we tested 11 commercial crustacean and five mollusc SPT extracts and found even greater, critical variability in their reliability,” said Andreas Lopata, one of the study’s corresponding authors.
The extracts were taken from manufacturers in the US, Spain, and Switzerland. The researchers found that the total protein content varied up to 14-fold in five shrimp (from at least three different species), four crab, two lobster, two oyster and three clam/scallop extracts from six different manufacturers.
They concluded that some SPT extracts lacked a sufficient amount and diversity of important shellfish allergens, meaning test results could provide a false negative, which has the potential to put lives at risk. On the basis of the findings in this study and their 2019 study, the researchers are calling for the worldwide standardization of allergen extracts.
“Standardization of allergen extracts is urgently needed to improve the accuracy and reliability of SPTs,” said Thimo Ruethers, lead author of the study. “Also, improvements in blood tests, along with region-specific allergen extracts with known quantities of clinically well-characterized allergen components, are critical to achieve considerable improvements in allergy testing.”
Allergen-specific IgE blood tests are useful when skin testing is not possible or has been inconclusive. A blood sample is taken and the level of an immunoglobulin associated with allergic reaction (allergen-specific IgE) is measured in a lab.
The standardization of allergen products, including extracts, has been discussed for many years, since the establishment, in 1980, of the World Health Organization and International Union of Immunological Societies (WHO/IUIS) Allergen Standardization Subcommittee. Despite this, allergen standardization in the US and Europe has not been achieved.
The study was published in the journal Allergy, and the video below, produced by the journal, describes the study’s findings and its importance in diagnosing shellfish allergies.
Source: James Cook University