Diagnosing a food allergy seems like it should be pretty straight-forward, right? First, patient eats food and gets symptoms. Second, patient sees doctor and gets tests which confirm or rule out food allergies. However, it’s not always that simple. In this article, we’ll explore some of the challenges with diagnosing a food allergy to understand how getting to an accurate diagnosis can be both a science and an art – and learn about how one group is working to spur innovation in this area.
Food allergy diagnosis involves a number of steps but should always start with a detailed history. The history should include things like what food was eaten, in what quantity, what symptoms occurred and how quickly they happened after eating the suspect food. Other things to consider are whether or not the individual was able to previously eat the potential allergen without trouble. Getting a useful and accurate history can be a challenge because people forget things as time passes, possibly misreporting the experience from weeks or months before the day of their appointment. In addition, most people don’t eat only one food at a time – mixed dishes or meals that contain multiple food allergens can make it difficult to determine which one has caused the problem. It’s important for the clinician to ask the right questions while taking a history.
Following the collection of a detailed history, the clinician (an allergist or primary care physician) will determine the utility of blood or skin tests. IgE blood tests are used to determine whether or not an individual is producing specific IgE to the potential allergen. Without IgE production, an individual does not have an IgE-mediated allergy. However, some people will produce IgE and never have clinical symptoms of a food allergy, considered false positive (meaning IgE is detected in the absence of clinically relevant allergy). In a skin test, a small amount of the allergen is introduced into the skin via a prick with a lancet. If a red bump pops up in that location, it will be measured and compared to a standard to determine the likelihood of allergy. The larger the wheal (the red bump), the more likely an individual is to have a food allergy. But as with the blood test, false positives are common. Both of these tests are very good at determining who does not have allergy, but on their own they are poor laboratory tests for determining who does. Both skin and blood tests have the potential to over-diagnose those with food allergies, especially when panel tests (tests for many foods at once) are used. Along with a history of reaction, blood and skin tests are helpful for getting to a diagnosis, but alone they are not diagnostic.
The gold standard for diagnosing a food allergy is an oral food challenge (OFC), whereby an individual eats the food that may be causing a reaction. The OFC is conducted in a medical office with supervision to watch for objective signs of food allergy. Medical supervision is important in case there is a serious reaction, which is the biggest downside to OFC. Not only is there a risk for severe reactions during OFC, which can cause a lot of anxiety for patients and families, they are also time consuming and sometimes aren’t covered by insurance. It can also sometimes be hard to find a practitioner who conducts OFC in their office.
As you can see, diagnosing a food allergy involves pulling together many different pieces of information to determine whether an adverse food reaction is truly a food allergy. One group is on a mission to help change the problem of diagnosis. Food Allergy Research Education (FARE), the country’s largest food allergy advocacy group, recently launched their FAITH Challenge, offering millions of dollars in grants via a competition amongst researchers around the world. According to the initiative’s website, their goal is clear: “The goal is to create a replacement for OFC that is highly sensitive and specific and has the potential to identify multiple allergens. It is easy to use, does not depend on sophisticated instrumentation, and provides clear results that are reproducible.”
Researchers around the world are on the hunt for new and novel diagnostic tools that can more accurately predict food allergies. Support from an organization like FARE can help spur innovation. Until an improved tool is available, clinicians continue to approach food allergy diagnosis as detectives, using the science and a little bit of art to arrive at a food allergy diagnosis.
- AAAAI Website. Food Allergy. Available at https://www.aaaai.org/conditions-and-treatments/library/allergy-library/food-allergy#:~:text=Diagnosing%20Food%20Allergies&text=Your%20allergist%20will%20take%20a,a%20food%20and%20any%20reaction.. Accessed May 3, 2021.
- Foong, R, et al. Improving diagnostic accuracy in food allergy. J Allergy Clin Immunol. 2021;9(1):71-80.
- Sicherer, S, et al. Critical issues in food allergy: A National Academies report. Pediatrics. 2017. Available at https://pediatrics.aappublications.org/content/early/2017/07/19/peds.2017-0194.full. Accessed May 3, 2021.