Citrus allergy is more complex than many have thought previously, new findings by a Canadian allergist suggest. A negative test for one species of citrus allergy doesn’t rule out a patient reacting to other types, even if the fruits are closely related genetically, according to Dr. Jason K. Lee.
Conversely, he says that an allergy to one type of citrus does not necessarily mean a patient will be allergic to all or even any of the rest.
“Most allergists have it set in their minds that doing a test for orange rules out an allergy to every other citrus. And that’s actually the way I used to practice, too,” says Lee, a specialist in clinical immunology and allergy based in Toronto. “What I do now is try to get the patient to be as specific as possible about the type of citrus fruit they had. If they actually bring the fruit in, that’s often the better way to test.”
In a December letter published in the Annals of Allergy, Asthma and Immunology, Lee details the experience he had diagnosing a patient who came to him reporting a reaction after eating clementines. The patient had had a history of anaphylaxis triggered by clementine, the small citrus that is a hybrid of the willowleaf mandarin and the sweet orange. She also reported to Lee that she has oral allergy syndrome (OAS) to ragweed- and birch-related foods.
Lee performed skin-prick tests with fresh clementine and other citrus fruits, including a commercial sweet orange extract, and confirmed the patient’s observations. The results, he says, have wider implications for how allergists diagnose citrus allergy.
“The take-home message is that all citrus fruits are not interchangeable in terms of what causes reactions and what doesn’t,” Lee says. The findings reveal how complex and unique allergies can be from person to person.
“You can’t rule out a citrus allergy by just testing for orange, which is what most allergists do in their practice,” he says. “You want to individualize every assessment.” For allergists and patients, that can mean setting aside some established wisdom and practices when faced with a difficult-to-diagnosis allergy.
“I learn the most from listening to patients’ histories very carefully,” Lee says. “For even an allergist to know what protein cross-reacts with what other protein, I’m constantly looking this stuff up.”
Lee also reminds those with OAS and pollen allergies to pay close attention if they’re eating a piece of fruit and begin to notice symptoms. The risk is low, but anaphylaxis is still possible for some individuals.
“For a minority of OAS patients, they can have upper airway symptoms, which could be life-threatening,” he says. “If you have a change in voice, difficulty swallowing, or if you’re light-headed or get shortness of breath, this is either a very large local reaction, or a systemic reaction. Those are the patients I would give an epinephrine auto-injector to, and advise extra caution.”