A deeper dive into shellfish allergy diagnosis

01 September 2023

Shellfish are the number one food-related trigger of fatal allergic reactions in Australia. Accurate diagnosis is vital for identifying appropriate management tools and preventing adverse health effects. However, new research shows that one of the most common methods for diagnosing food allergies can yield unreliable results.

Skin prick testing (SPT) is often the first-line diagnostic approach for identifying an allergy to animals, plants, drugs and other culprits. It involves a healthcare worker placing a drop of solution made from the suspected culprit on a person’s forearm or back and seeing if the body reacts; if the skin becomes red and swollen, the test is positive. It’s considered an affordable, accessible and low risk method.

In a recent study, a team led by Dr Thimo Ruethers and Professor Andreas Lopata from the Australian Institute of Tropical Health and Medicine (AITHM) and JCU Singapore’s Tropical Futures Institute (TFI), tested a number of commercial crustacean and mollusc SPT solutions used to diagnose shellfish allergies.

“We suspected that some extracts may not even contain the specific allergenic shellfish proteins (allergens) required for triggering a skin reaction that would suggest a patient is allergic or not. So, we purchased 16 SPT preparations from 6 different manufacturers and tested them using biochemical and immunological methods,” Dr Ruethers says.

“We did find a huge diversity in the overall allergen content; some extracts did not contain a sufficient amount of shellfish allergen components. Thus, diagnosis is largely hampered, and tests could return a false negative.”

A false negative SPT result can lead to life-threatening anaphylaxis if patients are exposed to food they are allergic to. Therefore, other diagnostic tests — such as oral food challenges in clinical settings — are often still required.

The study not only found that some commercial solutions lack a sufficient amount of shellfish allergens, but they also lacked diversity of shellfish allergens.

“Every single shellfish is different. This is important because, for example, if you test only for calamari and the patient is negative, they may be highly allergic to a different type of shellfish, such as prawns,” Dr Ruethers says.

“That’s only one element. We then must consider the diversity of each kind of shellfish across regions. The prawns we eat in Australia are quite different to those you would eat in Europe or North America. Yet, Australia’s commercial SPT extracts are produced and imported from Europe and North America.

“In this study, none of the prawn SPT extracts we analysed were a true reflection of prawns eaten in Australia.”

In 2019, Dr Ruethers, Professor Lopata and a team undertook a similar study, evaluating the effectiveness of 26 SPT extracts for fish allergy, and found considerable variability. They also discovered the critical importance of species-specific allergies.

“Both of these studies provide proof that commercial SPT solutions are not reliable for diagnosing fish or shellfish allergies,” Dr Ruethers says. “Standardisation of allergen extracts is urgently needed to improve the accuracy and reliability of SPT.”

Food allergies pose major public health concerns, lower quality of life and can be fatal. Professor Lopata says developing more reliable allergy diagnostic tools, including blood tests, requires further interdisciplinary research and is necessary to safeguard allergy sufferers globally.

“We want patients to be able to make informed decisions about their diet and at least be aware of what can happen. We need to be able to identify those at risk of anaphylaxis to ensure they have an emergency medication with them at all times. At the end of the day, it saves lives,” Professor Lopata says.

This research received funding from the National Health Medical Research Council (NHMRC). Dr Ruethers will present it as a Hot Publication at the upcoming ASCIA conference in Sydney (5-8 Sep) with the support of the Centre for Food & Allergy Research (CFAR).