The complexities of defining atopy in severe childhood asthma

Defining atopy in children with severe, therapy-resistant asthma is complex. There is currently no gold standard test; both skin prick testing (SPT) and allergen-specific IgE (sIgE) are used. Furthermore, atopy is increasingly considered to be a spectrum, not an all-or-none phenomenon.

SPTs and sIgE cannot be used interchangeably, and if both tests are not performed, opportunities for intervention will be missed. Furthermore, the severity of atopy will be defined differently by the two tests.

Cross-sectional study of 47 children with severe, therapy-resistant asthma, mean age 11.8 years, range 5.3-16.6 years, who underwent SPT, and measurement of total and sIgE as part of their clinical work-up.

Overall, 42/47 (89%) were atopic (defined as either one positive SPT or sIgE). There was 98% concordance between the two tests in classifying atopy. When each allergen was considered individually, in 40/200 (20%), the SPT and sIgE results were discordant, most commonly in 25/200 (12.5%), the SPT was negative and the sIgE was positive. House dust mite and cat sensitization were more likely detected by sIgE, but dog sensitization by SPT. When atopy was quantified, the sum of sIgEs compared with the sum of SPT weal diameter showed a moderate correlation (r(2) =0.44, P<0.001). Total IgE increased with an increasing number of positive sIgEs (P=0.028), but not significantly with increasing numbers of positive SPTs.

SPT and sIgE identify group prevalence of atopy equally well; however, for individual allergens, concordance is poor, and when used to quantify atopy, SPTs and sIgE were only moderately correlated. In a clinical setting, if allergen avoidance is contemplated in children with severe, therapy-resistant asthma, both tests should be performed in order to detect sensitization.