Age and lung function were reported in all included studies, serum IgE levels were reported in four studies,[8,10–12] smoking history were reported in 3 studies,[10–12] duration of asthma was reported in three studies,[8,12,13] serum eosinophil levels were reported in 2 studies,[10,11] and frequencies of asthma exacerbations were reported in 3 studies.[10–12] The characteristics of all included studies are summarized in Tables 1 and 2. Here, IGHE is linked to asthma.