October 17, 2020
A shrimp allergy test delivered with a dab of shrimp extract in the nose is safe and reliable, Barcelona researchers report.
The test provides 90% sensitivity and 89% specificity with a positive predictive value of 90%.
For those patients who fear anaphylactic shock during a food challenge test, this could prove game changing. "With our test, symptoms went away with no antihistamines or corticosteroids even in participants that had a reaction," Sònia Gelis, PhD candidate, University of Barcelona, Spain, told Medscape.
The new shrimp nasal challenge test was described in a live presentation at the online FAAM-EUROBAT Digital meeting.
In an interview with Medscape earlier this week, Gelis explained, "We don't normally do an oral food challenge for shrimp -- it's expensive and can lead to anaphylaxis. Most patients who are sensitized simply avoid it." The new test would provide proof of who is shrimp-sensitized, who is shrimp-allergic, and who is not allergic, offering patients better understanding of their status and tolerance, she said.
Shrimp Extract in the Nostril
Investigators enrolled 44 participants who were all confirmed as shrimp-sensitized with a positive skin prick test. Twenty participants were sensitized but tolerant, and 22 were allergic. They were divided into placebo and control groups. A shrimp extract was prepared in three different concentrations: 1:100, 1:10, and 1:1.
Each participant was presented with a baseline challenge with a saline solution on the inferior turbinate of both of their nostrils. Two participants from each group were eliminated when they reacted to the saline.
In the remaining participants, researchers introduced the three concentrations of shrimp extract in sequence. "We continued the challenge with a higher concentration each time if there was no reaction. The last challenge was not diluted," Gelis said.
Investigators used acoustic rhinometry (an objective scale) and the visual analogue scale (a subjective scale) after each test.
The test proved to be safe. Pruritus and obstructed nose were common reactions. "But those symptoms disappeared within 15-45 minutes," Gelis told Medscape. The researchers did not see any significant secondary adverse events or reactions that required medication.
No one in the shrimp-sensitized group reacted and only two of the 18 participants had a positive result. In the shrimp-allergic group, only two of the 20 participants had a negative test. "Thus we see that only the really allergic have a local inflammatory reaction," Gelis said. "We established that the nasal challenge is both quick and safe." The entire test took about 4 hours, much less time than the typical food challenge, which can take a whole day or several days.
According to Margitta Worm, MD, PhD, University of Berlin, Germany, who was not involved in the study, the investigators seemed a bit overenthusiastic about their results, given the small number of patients studied. "But for an exploratory study the results are quite promising. We look forward to hearing more about it."
Nevertheless, the research team is already using the nasal challenge in practice at the University of Barcelona hospital. "The next step will be to make this test available to more people and other centers. It has the potential to help diagnose shrimp allergy around the world," Gelis said.
Shrimp is one of the main causes of food allergy, with a worldwide prevalence of 5.4%. "It's the third most prominent food allergy in adults in Spain," Gelis said. "But we can't prove how bad it is. We can't do a food-challenge diagnosis because we don't have the resources," that makes it difficult to differentiate people who are shrimp-allergic from those who are merely shrimp-sensitized. The Barcelona researchers' new nasal challenge test has the potential change that.
Ingrid Hein is a freelance health and technology reporter based in Hudson, Quebec.
Gelis and Worm have disclosed no relevant financial relationships.