Allergy indices based on allergen dose-response curve in a randomly selected sample of schoolchildren

Skin-test sensitivity was computed in 61 schoolchildren drawn from a stratified random sample in order to generate two allergy indices based on a quantitative skin-test assay: Individual Allergy Index (IAI) and Population Allergy Index (PAI). The former to quantitate IgE-mediated skin test sensitivity of each subject, the latter to describe the degree of skin reactivity of our sample to a single allergen. Five allergen extracts were tested at 4-fold dilutions. Sensitivity endpoint data were used to generate IAI. Frequency distribution of IAI seemed to be bimodal as asymptomatic subjects gathered at the lower part while symptomatic children showed a peak in the middle. By means of criteria based on the relation between IAI and the prevalence of symptoms we were able to classify atopy in five classes from normal (all asymptomatic subjects) to severe atopy (all symptomatic subjects). Each positive reaction was plotted as a function of the allergen concentration eliciting the weal, and linear regression with confidence limits was calculated for grass and Dermatophagoides pteronyssinus only. PAI was represented by the slope, which depends on the reactivity of the sample, and the intercept, which involves the potency of the allergen as well. Grass and D. pteronyssinus showed the same slope while the intercepts differed. The slope increased if we considered symptomatic subjects only. We propose both these indices for clinical and epidemiological studies.