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.

Contact urticaria from carboxymethylcellulose in white chalk.

BACKGROUND: Carboxymethylcellulose (CMC) is widely used in consumer goods, foods, and medicaments as a binder, emulsifier, and viscosity enhancer. Cases of immediate and delayed allergic reactions to this anionic cellulose polymer have been reported. OBJECTIVE: To report a case of contact urticaria from CMC in chalk, with possible cross-reaction to methyl hydroxyethylcellulose (MHEC). METHOD: Patch tests with readings at 48 and 96 hours were performed with the North American Contact Dermatitis Group standard series and benzisothiazolinone. Open and prick tests with readings after 30 minutes were performed with two brands of chalk as well as with various petrolatum and aqueous dilutions of CMC, MHEC, oleic acid, and calcium carbonate. RESULTS: The patient developed strong urticarial reactions during open tests with both powdered chalks and had milder reactions to the open test with CMC 10% aqueous (aq) and to prick testing with CMC 0.1% aq. No reaction to MHEC or any of the other ingredients of the chalks was observed. No relevant delayed reaction was noted. CONCLUSION: CMC can cause contact urticaria. It remains unclear why our patient reacted more strongly to the chalk than to CMC itself. We speculate that the abrasive nature of the chalk enhances the cutaneous penetration of CMC or that calcium carbonate, the main ingredient of the chalk, acts as an adjuvant. It is also possible that CMC and MHEC cross-react and that our negative results with MHEC may be due to improper testing technique or concentrations.