D1.11 - Determinants of allergen sensitization and wheal size variability in skin prick testing in a large outpatient cohort

Skin prick testing (SPT) is a cornerstone in the diagnosis of IgE-mediated allergic disease; however, the determinants of allergen wheal size variability are not fully understood. This study aimed to evaluate the association of demographic factors, seasonality, and histamine reactivity with allergen sensitization and wheal size.

A retrospective study included all outpatients, 0 to 88 years, evaluated for rhinitis and/or asthma who underwent SPT with a standardized aeroallergen panel over a 17-year period. Sensitization was assessed using multivariable logistic regression models, and allergen-specific linear regression models were fitted to evaluate the association of wheal size with age group, sex, season, and histamine wheal size.

Overall, 5,310/8,552 patients (62.1%) were sensitized; median age was 30 (IQR 12–46) years and 51.9% were male. Sensitization rates and mean wheal sizes varied across allergens and demographic strata. Sensitization showed age-related patterns independent of birth cohort, with early peaks for house dust mites, early adulthood peaks for grasses, Olea europaea and animal dander, and later peaks for Cupressus and Parietaria. Age group was the most consistently retained predictor of sensitization, whereas sex, seasonality, and histamine reactivity showed allergen-specific effects.

Among sensitized individuals, histamine wheal size was consistently and positively associated with allergen wheal size across all allergens (β range: 0.17–0.55 mm per 1-mm increase; all p<0.001). Sex-related differences were observed for most allergens, generally with larger wheal sizes in males. Age showed a clear association with wheal size for house dust mites and moulds, while age-related effects were less evident for animal dander and pollen allergens. Seasonal effects were modest. Overall, model explanatory capacity was limited (adjusted R² approximately 2–14%). Results are summarized in Table 1.

Sensitization rates vary across age and show allergen-dependent associations with sex, seasonality, and histamine reactivity. Among sensitized individuals, allergen wheal size is strongly related to histamine reactivity, while demographic and seasonal factors exert heterogeneous, allergen-dependent effects and explain only a small proportion of wheal size variability, supporting a predominant role of individual susceptibility in SPT responses.