Supplementary Material for: Specific IgE to Total IgE Ratio Does Not Improve Peanut Diagnostic Accuracy in Adults

Background: Peanut specific IgE (sIgE) can lead to false-positive results. Objective: We aimed to assess whether peanut sIgE to total IgE (tIgE) ratio improves accuracy in predicting clinical reactivity to peanut compared to peanut sIgE alone, which has not been explored in the adult population so far. Method: A retrospective chart review was performed for adults who underwent peanut oral food challenge (OFC) and/or oral immunotherapy (OIT) at the Centre Hospitalier de l’Université de Montréal’s allergy clinic between January 2017 and July 2021. Patients with positive peanut OFC and/or undergoing OIT were considered peanut-allergic. Patients with negative OFC were considered peanut-tolerant. Peanut sIgE to tIgE ratios were calculated and performance characteristics of the sIgE to tIgE ratio were compared to sIgE alone by using receiver operator characteristics curves. Results: Forty-two patients were included (52% male) with a median age of 26 years (range 14–54). Forty-five percent had atopic dermatitis. Median sIgE levels were 2.64 kUA/L (range 0.1–100), median tIgE levels were 154 kUA/L (range 19–3,400), and median sIgE to tIgE ratio was 0.66% (range 0.04–38.3). Twenty-four patients (57%) were classified as peanut-allergic and 18 (43%) as peanut tolerant. The area under the curve for peanut sIgE was 0.921 compared to 0.926 for peanut sIgE/tIgE (p not statistically significant). Conclusions: We found that there was no significant benefit in using peanut sIgE to tIgE ratio over sIgE alone to predict peanut reactivity in an adult population. Larger prospective studies are needed to further confirm these findings.