Immunoglobulin E as a biomarker for the overlap of atopic asthma and chronic obstructive pulmonary disease

Asthma-COPD overlap (ACO) is a common clinical syndrome, yet there is no single objective definition. We hypothesized that Immunoglobulin E measurements could be used to refine the definition of ACO. In baseline plasma samples from 2870 subjects in the COPDGene Study, we measured total IgE levels and specific IgE levels to six common allergens. Compared to usual COPD, subjects with ACO had higher total IgE levels (median 67.0 vs 42.2 IU/ml) and more frequently had at least one positive specific IgE (43.5 vs 24.5%). We previously used a strict definition of ACO in subjects with COPD, based on self-report of a doctors diagnosis of asthma before the age of 40. This strict ACO definition was refined by the presence of atopy, determined by total IgE >100 IU/ml or at least one positive specific IgE, as was a broader definition of ACO based on any asthma history. Subjects will all three ACO definitions were younger (mean age 60.0-61.3), were more commonly African American (36.8-44.2%), had a higher exacerbation frequency (1.0-1.2 in the past year), and had more airway wall thickening on quantitative analysis of chest CT scans. Among subjects with clinical ACO, 37-46% did not have atopy; these subjects had more emphysema on chest CT scan. Based on associations with exacerbations and CT airway disease, IgE did not clearly improve the clinical definition of ACO. However, IgE measurements could be used to subdivide subjects with atopic and non-atopic ACO, who might have different biologic mechanisms and potential treatments.