With an increasing incidence of food allergies worldwide, it is important that clinicians—and particularly GI specialists—are equipped to identify and manage these patients in clinical practice.
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“Approximately 30-35% percent of GI patients self-report having a food allergy, which speaks to the fact that food is a major trigger for GI symptoms,” says Anthony Lembo, MD, Department of Gastroenterology, Hepatology & Nutrition, Cleveland Clinic, while also noting that 2-4% of individuals receive a formal diagnosis.
Recently, Dr. Lembo presented on this topic, “Food Allergy Testing: If, When and How to Do It,” during the American College of Gastroenterologists conference. His discussion offered colleagues insights into food allergy pathophysiology, how to approach testing in the clinical setting and common misconceptions that must be addressed.
To successfully identify and care for patients with food allergies, clinicians must first understand the pathophysiology of food allergies and how they present. It is also important to recognize the difference between food allergies and food intolerances.
“A food allergy is an adverse immune response to food protein and includes IgE-mediated allergies which occur rapidly (minutes to few hours) or cell-mediated allergies that causes chronic symptoms (i.e., Celiac disease),” explains Dr. Lembo. “The most common food allergens (90%) include milk, eggs, wheat, soy, peanuts, tree nuts, fish and shellfish. Of these, peanuts, tree nuts, fish and shellfish are the most severe and life-threatening.
“On the other hand, food intolerances are not allergies, and many people have sensitivities to certain foods in varying degrees,” he continues. “A common example is lactose intolerance, which an estimated 65 percent of the world population has difficulty digesting. Other types of intolerances include caffeine, alcohol, histamine, sulphites and salicylates.”
Clinical manifestations can vary depending on the type of food allergy (IgE- vs. cell-mediated). However, some of the common presentations include skin issues such as urticaria, angioedema, pruritus, flushing, rash, atopic dermatitis, eczema and respiratory symptoms (i.e., cough, wheezing, rhinitis). GI symptoms, according to Dr. Lembo, are the primary sign in 50% of patients. This can include swelling of lips, diarrhea, cramps, bloating, etc.
Symptoms that are most likely not the result of a food allergy include the following: headaches, mood changes, chronic nasal congestion, reactions that occur intermittently to a specific food, hives that occur for more than a day, variable symptoms, fatigue, brain fog, runny nose and symptoms that present hours to days following ingestion.
Diagnosing food allergies can be challenging, Dr. Lembo notes. “This is, in part, due to non-specific symptoms, including GI, skin, respiratory and systemic issues,” he explains. “Additionally, with multiple foods in our diets, it can be difficult to isolate the specific allergen.”
When a food allergy is suspected, testing may be warranted; however, the tests are not always definitive Dr. Lembo acknowledges while referencing the sensitivity/specificity (50%/90%) and potential for false positives/false negatives.
Depending on the patient an oral food challenge is often considered the standard approach, according to Dr. Lembo, who notes that an allergist should conduct this diagnostic test. An oral food challenge involves receiving the suspected allergen in increasing doses and if an individual shows signs of a reaction the test is stopped.
Other common food allergy tests include skin prick tests, allergen-specific immunoglobulin E (IgE) tests and elimination diets. Patch testing is another option, but Dr. Lembo says that this is not widely used due to variable sensitivity and specificity.
There are five allergy tests that are not recommended under current guidelines. These include IgG testing, cytotoxic food testing, provocation-neutralization testing, antigen leukocyte cellular antibody test (ALCAT), and hair analysis or electrodermal testing.
Results from a recent study conducted by Dr. Lembo and colleagues suggest an IgG-guided elimination diet shows promise for irritable bowel syndrome; however, he notes, further exploration is needed before a recommendation for this test can be made.
When a patient shows signs of a food-related reaction with GI involvement, the gastroenterologists must first determine if their symptoms suggest an IgE-mediated food allergy (i.e., reproducible symptoms, immediate, common allergen, etc.), explains Dr. Lembo.
“If the answer is yes, they should be referred to an allergist who will conduct the necessary testing,” he says. “For everyone else, you should consider other conditions such as celiac disease, eosinophilic gastrointestinal diseases (EGIDs) or eosinophilic esophagitis (EoE). In these cases, collaboration with an allergist is warranted to address the allergic component.”
Gastroenterologists have an important role to play in not only caring for patients, but also helping them better understand food allergies and intolerances. This includes addressing common misconceptions that can cause confusion and lead patients down the wrong path.
One such “food allergy myth,” according to Dr. Lembo, is that food allergy reactions get more severe each time they occur. “This isn’t actually true. There are many co-factors that can worsen severity such as exercise, amount ingested, or acute illness.”
“Another myth is that infants should not eat common food allergens,” he adds. “There has been increasing education on this, so hopefully most people today know this isn’t true. Guidelines recommend feeding allergenic foods to babies starting around four to six months as a way to prevent food allergies from developing.”
When asked what he wants fellow gastroenterologists to take away from this discussion, Dr. Lembo emphasizes the importance of recognizing food allergies and how they present in clinical practice.
“Food allergies are becoming increasingly common, and as clinicians, we should be aware of the signs and symptoms that may suggest a food allergy,” he notes. “Additionally, we must also know when a referral to an allergy specialist for testing is appropriate. Working collaboratively is important for comprehensive patient care.”