Do We Need an Oral Food Challenge (OFC) or Food Oral Immunotherapy (OIT)?
One of the most common concerns we face in allergy practice is reflected in this typical scenario: “My 5-year-old son has had positive skin and blood tests for peanut allergy since he was an infant. He never had peanuts and we do not know how he would react to peanuts. What do we do next?”
As allergists with experience in oral food challenges and food oral immunotherapy, we are well-positioned to help answer this question. Not every positive skin test or blood test reflects a true clinical allergy to peanuts. Many children have been advised to avoid foods based on allergy skin tests or blood tests alone and may be unnecessarily avoiding foods to which they don’t actually have a true allergy. An oral food challenge (OFC) is the gold standard to help determine whether actual allergy exists.
Let’s first explore the definitions of oral food challenge (OFC) vs. food oral immunotherapy (OIT). The OFC is a diagnostic test whereas food OIT is a treatment. An OFC is planned when the allergy skin and/or blood tests do not give a clear answer about the presence or absence of true food allergy. Food OIT should be pursued only after clinical allergy has been definitively established and there is a desire for an active desensitization therapy. To be clear, this does not mean that an OFC is always needed before food OIT. In many cases, there is a clear clinical history of reaction which is confirmed by the testing. However, in cases where there is no history of consumption of the food (just positive tests) or the reaction was a long time ago and the testing has now become negative or very low, an OFC is very helpful before committing to OIT (since OIT may not actually be needed).
The diagnostic OFC typically requires a single visit over several hours to determine if a child will react to a food given a controlled clinical setting. The food dose is measured for each step and started at a very small dose for safety. If there are no signs or symptoms of a reaction after the first dose, the next dose is given after 15-30 minutes. Similar steps are repeated every 15-30 minutes until the predetermined full amount has been given. The patient is closely observed for another 1-2 hours to ensure the absence of any symptoms. A successful (non-reactive) challenge means the absence of true food allergy. It’s important to understand that a passed challenge means the child can consume the food, in spite of any previously positive allergy tests. A passed challenge is the gold standard for the lack of clinical food allergy.
The OFC can be done as an open challenge where everyone knows about the food and the amount given. It can also be done as single-blinded where the patient or family does not know what food is being given but the medical team is aware. For research, it can be done as double-blinded, where neither the patient nor the medical team administering the food knows about the food being administered. Only the research team that prepares the food will know about the contents. In most cases in private practice, an open challenge would usually be chosen.
The main purpose of an OFC is to assess whether a true allergy exists when testing is equivocal or there is no history of consuming the food. However, it may also be appropriate even when it’s very likely that a patient would tolerate a food in order to reassure parents that the food is safe. Finally, in a research setting, an OFC is sometimes used even when it’s known that a child will almost certainly react but done purposely to establish the “eliciting dose” that causes the reaction.
By contrast, food oral immunotherapy (OIT) is a food allergy treatment for those who have a definite food allergy, which has been established by a clear clinical history of reaction and positive testing, or, in some cases, a failed food challenge. The purpose of OIT is to increase the threshold of reactivity and to reduce the risk of reactions from accidental food exposure. Over time, some patients may reach free eating and tolerance, though this is not always practical for all patients and all foods. In many cases, “bite-proof” dosing is more appropriate. Food OIT is a treatment that requires significant time, resources, and commitment.
OIT is started with at a vastly lower dose than that used in a challenge. For example, the first OIT visit might finish at 2 mg of peanut protein, whereas in a challenge 6000 mg of peanut protein may be consumed. In OIT, the patient typically takes a daily dose at each level for 1-2 weeks. The next, slightly higher dose is given under medical supervision in the office and if tolerated, this level is then continued at home for the same interval. Dose increases are never performed at home. Depending on the goal dose, it may take anywhere from several months to over a year to reach a pre-planned maintenance dose for OIT. If freely eating is planned, a full serving OFC may be required at the end of the dose-escalation steps.
Now, let’s revisit the starting question. This 5-year old has positive allergy skin and blood tests for peanut allergy but has never had peanut exposure, so we do not know if he has a true peanut allergy or not. Depending on the level of the skin and blood tests, the allergist may feel confident that true allergy is highly likely but if the tests are intermediate, an OFC to peanut under close medical supervision can help establish true allergy or not. If the child eats a full portion of peanuts by the end of the OFC and has no reaction, he will be considered not allergic to peanuts. At that point, he will have the freedom to introduce peanut into the diet. If the child does react during the OFC, he will need to continue avoiding peanuts. The family can also consider food OIT as an option for desensitization in this scenario.
Both an OFC and food OIT involves a risk of reaction, including possible severe reactions. They should always be done by an allergist with the knowledge, experience, and infrastructure to manage these risks. And of course, a family should have a thorough discussion with the treating allergist before either an OFC or food OIT is undertaken to get a full perspective on the risk involved, the rationale for the procedure, and the benefits of proceeding with the procedure.
Atul N. Shah, MD, FACAAI, FAAAAI
New York Food Allergy & Wellness