Age, sex and the association between skin test responses and IgE titres with asthma.

BACKGROUND

Skin prick tests (SPTs) and allergen-specific serum IgE (sIgE) measurements are the main diagnostic tools for confirming atopic sensitization. Results are usually reported as 'positive' or 'negative', using the same arbitrary cut-offs (SPT>3 mm, sIgE>0.35 kUA /l) across different ages and sexes. We investigated the influence of age and sex on the interpretation of allergy test in the context of childhood asthma.

METHODS

In a population-based birth cohort (n = 1051), we ascertained the information on asthma/wheeze (validated questionnaires) and performed SPTs and sIgE measurement to inhalant allergens (dust mite, cat, dog) at follow-ups between ages three and 11 years. We investigated the association between quantitative sensitization (sum of SPT mean wheal diameters [MWD] and sIgE titres to the three allergens) and current wheeze and asthma across ages and sexes.

RESULTS

We observed a significant association between the SPT MWD and sIgE titres and wheeze/asthma at most ages and for both sexes. However, the strength of this association was age- and sex-dependent. For SPTs, the strength of the association between MWD and asthma increased with increasing age; we observed the opposite pattern for sIgE titre. For any given SPT MWD/sIgE titre, boys were significantly more likely to express clinical symptoms, particularly in early life; this difference between males and females diminished with age and was no longer significant by age 11 years.

CONCLUSIONS

Age and sex should be taken into account when interpreting the results of skin tests and sIgE measurement, and age- and sex-specific normative data are needed for these allergy tests.