Background:The heterogeneity and lack of validation of existing severity scores for food allergic reactions limit standardization of case management and research advances.Objective: To develop and validate a severity score for food allergic reactions.Methods: Following a multidisciplinary experts consensus it was decided to develop a food allergy severity score (FASS) with ordinal (oFASS) and numerical (nFASS) formats. oFASS with 3 and 5 grades were generated through expert consensus, and nFASS by mathematical modeling. Evaluation was performed in the EuroPrevall outpatient clinic cohort (8232 food reactions) by logistic regression with request of emergency care and medications used as outcomes. Discrimination, classification and calibration were calculated. Bootstrapping internal validation was followed by external validation (logistic regression) in 5 cohorts (3622 food reactions). Correlation of nFASS with the severity classification done by expert allergy clinicians by Best-Worst Scaling of 32 food reactions was calculated.Results: oFASS and nFASS map consistently, with nFASS having greater granularity.With the outcomes emergency care, adrenaline and critical medical treatment, oFASS and nFASS had a good discrimination (receiver operating characteristic area under the curve [ROC-AUC]>0.80), classification (sensitivity 0.87-0.92, specificity 0.73-0.78) and calibration. Bootstrapping over ROC-AUC showed negligible biases (1.0×10 -6 -1.23×10 -3 ).In external validation nFASS performed best with higher ROC-AUC. nFASS was strongly correlated (R 0.89) to best-worst scoring of 334 expert clinicians. Conclusion:FASS is a validated and reliable method to measure severity of food allergic reactions. The ordinal and numerical versions that map onto each other are suitable for use by different stakeholders in different settings.

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Background There is increasing interest in the use of eliciting doses (EDs) to inform allergen risk management. The ED can be estimated from the distribution of threshold doses for allergic subjects undergoing food challenges within a specified population. Estimated ED05 values for cow's milk (the dose expected to cause objective allergic symptoms in 5% of the milk‐allergic population) range from 0.5 mg to 13.9 mg cow's milk protein. We undertook a single‐dose challenge study to validate a predicted ED05 for cow's milk of 0.5 mg protein. Methods Participants were recruited from 4 clinical centres. Predetermined criteria were used to identify patients reacting to 0.5 mg cow's milk protein (approximately 0.015 mL of fresh cow's milk). Children over 1 year underwent formal challenge to cow's milk to confirm clinical reactivity. Results 172 children (median age 6.0 (IQR 0.7‐11) years, 57% male) were included in this analysis. Twelve (7.0%, 95% CI 3.7%‐11.9%) children experienced objective symptoms that met the predetermined criteria. One participant had mild anaphylaxis that responded to a single dose of adrenaline, the remainder experienced only mild symptoms with no treatment required. We did not identify any baseline predictors of sensitization that were associated with objective reactivity to the single‐dose challenge using 0.5 mg cow's milk protein. Conclusions These data support an estimated ED05 for cow's milk of 0.5 mg protein. Values for ED05 above 0.5 mg for cow's milk protein proposed for allergen risk management need to be reviewed.

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