In recent years, clinicians and patients alike have experienced both significant interest in and confusion around food allergies/sensitivities and their manifestations in the gastrointestinal tract. A lack of clarity has led to frustration, inappropriate testing, and missed diagnoses.
Medscape contributor Akash Goel, MD, a clinical assistant professor of medicine at Weill Cornell Medicine, spoke with Clifford Bassett, MD, the founder and medical director of Allergy & Asthma Care of New York, a clinical assistant professor at NYU Grossman School of Medicine, a faculty member of the Weill Cornell Medical College in New York City, and author of The New Allergy Solution, about working toward a framework with which to approach diagnostic dilemmas around these food-related conditions.
Weighing Testing Options
There are various types of testing. When should they be used, and how should they be interpreted by gastroenterologists?
I have found that a true collaboration with my gastroenterologist colleagues has led to greater patient satisfaction; better diagnostic accuracy; and improved co-management, including appropriate follow-up care.
Allergists strive to focus on choosing proper diagnostic tools as well as clinical correlation in the evaluation of food allergy. Another emphasis is the use of patient educational resources and in-depth counseling to mitigate exposure to the offending foods. Furthermore, using the skills of an experienced registered dietitian can optimize proper nutritional guidance for our patients.
To confirm that a true food allergy exists and to avoid unneeded food restrictions, it is preferable to have a consultation with an allergist.
When the pretest likelihood of a food-induced type 1 reaction is high (eg, classic immediate allergic symptoms, such as hives, wheezing, itching, or immediate emesis), an IgE food allergen test is indicated.
In most cases, a very sensitive method in type 1 IgE-mediated food allergy diagnostic testing is a reproducible food prick test, with either a commercial-grade allergenic extract or a fresh food. Prick food testing typically would be administered by the consulting allergist, who would interpret the results.
A negative food prick test generally has a very high predictive value, indicating a low likelihood of a true type 1 food allergy.
A positive food skin prick test or an in vitro IgE food-specific test may indicate allergic sensitivity; however, the individual's clinical response to a food, along with the characteristic signs and symptoms, is required for diagnosis of food hypersensitivity.It is important to note that the size of the food skin test does not necessarily correlate with severity of symptoms for that patient, but it does indicate a greater likelihood of a clinical allergy.
When it comes to the methods of diagnostic evaluation, food skin testing is generally preferred. Other diagnostic testing includes serologic food-specific IgE (ImmunoCAP) assays.
With both methods, a positive food test does not imply an individual has a clinical food allergy. A complete patient clinical history is necessary to properly interpret testing and consequent future recommendations.
Immunoassays are in vitro allergen antibody tests to measure food-specific IgE in the serum. A greater "likelihood" may exist of a food-induced reaction with higher levels of food-specific IgE values. However, the food-specific IgE level (ranging from low to high) does not automatically correlate with severity of a food-induced reaction.
To reiterate, this underscores the importance of an accurate patient clinical history to allow for proper test interpretation.
Testing can be particularly useful at times, because it is not affected by various medications an individual may be taking, such as antihistamines, in those with a history of severe anaphylaxis, nor by testing in a patient who has active urticaria and dermatographia.
Currently, food component IgE can be used in an adjunctive fashion in patients with suspected peanut, tree nut, cow's milk, or egg allergy by helping to define potential severity of a food allergic reaction, because it is testing for specific proteins in a food.
Allergists may also consider specific food predictive levels in children, depending on the clinical situation.
In some cases when the diagnosis is in doubt and the clinical suspicion for a true food allergy is relatively low, an oral food challenge may be considered under appropriate medical supervision.
Current and Future Treatment Options
What types of drugs, technologies, and assays are in the pipeline for food allergy and sensitivity testing?
In 2020, the US Food and Drug Administration approved the first biologic drug for oral immunotherapy for children and adolescents with a confirmed peanut allergy. Oral immunotherapy involves in-office initiation and every 2 weeks up dosing combined with an at-home process, whereby gradually escalating dosages of a food allergen are ingested over time until a steady maintenance dose is reached.
Researchers are looking at other routes of allergen delivery, such as sublingual immunotherapy and epicutaneous immunotherapy. The goal is to provide a form of allergen-specific immunotherapy to modify a food allergen response, allowing the individual to become more tolerant to a selected food and/or desensitization.
What's your perspective on the role of food as a driver of functional bowel diseases, like IBS?
Nearly 20 years ago, observations of inflammation in IBS challenged its traditional classification as a functional disorder. Half or more of those carrying this diagnosis report that foods can aggravate their symptoms. This association has traditionally been viewed as food intolerance, because testing efforts in search for type 1 and type 3 allergies have generally failed to implicate these allergic mechanisms.
Recent studies, however, resurrect a role for true food allergies. In one study, food-induced abdominal pain has been observed in association with local IgE production in response to food antigens, creating new potential therapeutic options.
Other studies (from 2013, 2018, and 2021) using skin patch testing implicate type 4 allergies in some cases. In these studies, participants with IBS are patch-tested to an extensive panel of type 4 food allergens. The foods that elicit allergic reactions in the skin are subsequently eliminated from the diet, and a significant percentage of those tested experience moderate to marked improvement or complete relief of their IBS symptoms.
It is theorized that a type 4 allergic reaction similar to that elicited in the skin by the patch testing occurs in the intestinal lining when the same foods are ingested, triggering IBS symptoms. Patch testing to a comprehensive set of type 4 food allergens may provide a new approach to the evaluation and management of IBS.
It is likely that IBS has several different underlying causes, some allergic in nature, all resulting in its well-characterized symptom complex.
Follow Medscape on Facebook, Twitter, Instagram, and YouTube
