Study: Anaphylaxis Is Rare During Clinic-Based, Non-Research Oral Food Challenges
A September 2017 study in Annals of Allergy, Asthma and Immunology reported that open oral food challenge (OFC) is a relatively safe procedure that offers benefit to patients. The gold standard test to detect food allergy is a double-blind placebo-controlled OFC, in which neither the doctor nor the patient knows whether the patient is consuming allergen or a harmless substitute (the placebo).
In an open OFC, unlike a blinded OFC, no placebo is used; both the doctor and the patient know the patient is eating allergen. However, the patient’s knowledge can sometimes lead to a false positive test result. If anxiety causes the patient to have symptoms resembling an allergic reaction, the test can indicate an allergy even though the patient is not actually allergic. The false positive rate for open OFCs is higher than for blinded OFCs. However, open OFC is more commonly used in a clinical setting because it is faster and requires less staffing.
Between 2008 and 2013, data were collected for nearly 6,400 open OFCs conducted at five academic food allergy centers, representing five regions in the U.S.:
- Texas Children’s Hospital Food Allergy Program
- University of Pittsburgh School of Medicine, Children's Hospital of Pittsburgh of University of Pittsburgh Medical Center
- Riley Hospital for Children at Indiana University Health
- University of Washington School of Medicine, Northwest Asthma & Allergy Center
- Boston Children's Hospital
Eighty-five percent of the patients were under age 18. A range of raw and baked allergenic foods were tested. Most, but not all, of the OFCs were considered low risk because patients hadn’t reported recent reactions, had a history of tolerating the tested food, had low levels of IgE antibodies to that food, or had IgE antibody levels suspected to result from cross-sensitization (that is, reactivity to a different allergen).
Some, but not all, of the patients had positive skin prick test results prior to their OFC. Historically, about 50 to 60 percent of skin prick tests and blood tests for food allergy have been found to give false positive results, in which the tests indicate the presence of food allergy even though the patient can eat the food without reacting. High false positive rates for skin prick and blood tests are among the reasons that researchers are interested in assessing the safety of OFCs.
In the study, the rate of allergic reactions observed during 6,377 OFCs was estimated at 14 percent. Two percent of the OFCs resulted in anaphylaxis. Of the 3,127 OFCs for which treatment data was available, 14 percent required treatment, most frequently with antihistamine, which was given in three-quarters of treated reactions.
Epinephrine was given for 14 percent of the treated reactions. Sixty-three OFCs, or roughly one percent of OFCs in the study, resulted in epinephrine treatment. Nineteen reactions resulted in hospitalization. Previous reports of anaphylaxis risk for non-research OFCs ranged from 6 to 33 percent. This difference may reflect that the patient population in this study included many patients described as low risk.
The finding that most patients (86 percent) completed the OFC without an allergic reaction suggests that, at least among diagnosed patients considered to be at low risk, a significant fraction may not have clinical allergy, for example, because they have outgrown a previous allergy or because their diagnosis was based on false positive test results. When food allergy is diagnosed inaccurately, quality of life suffers. Avoiding foods that can safely be eaten leads to needless anxiety and exclusion. Free-from foods are typically more expensive and less widely available. And removing common food allergens from the diet can increase the risk of nutrient deficiencies. The study concludes with the recommendation that open OFC is generally safe and that allergists should use this diagnostic test when indicated.