The food challenge risk index: Predicting positive open food challenges to milk, egg, and peanuts in children

Suspected food allergy is commonly encountered. Diagnosis requires skin testing, food-specific immunoglobulin E (IgE), and ultimately a food challenge. Previous studies determined food-specific IgE threshold levels predicting greater than 95% of the patients with a positive food challenge. However, if the food-specific IgE level is less than the threshold, a food challenge is required. Oral food challenges are time consuming, and they subject patients to allergic reactions. The aim of this study was to develop a food challenge risk index (FCRI) to predict positive food challenges. Fifty-five open food challenges were reviewed retrospectively. Skin prick tests, food-specific IgE levels, and time since last reaction were employed to develop a formula. The FCRI = [3 × skin prick test wheal (mm) + 10 × food-specific IgE level - time since last reaction (months)]. The FCRI value was compared to the food challenge results. Threshold levels chosen were 15, 20, and 25 for milk, egg, and peanut, respectively. Comparison of the FCRI to the actual food challenges across all groups revealed a sensitivity of 0.842 and a specificity of 0.861. We have derived a simple and accurate formula that uses readily available clinical data to predict positive food challenges. The FCRI may be used in a prospective fashion to reduce number of food challenges necessary for diagnosis of milk, egg, and peanut allergies in children.