A population-based clinical study of allergic and non-allergic asthma

The aim of this study was to describe differences between allergic and non-allergic asthma in a large community-based sample of Danish adolescents and adults.

A total of 1,186 subjects, 14 to 44 years of age, who in a screening questionnaire had reported a history of airway symptoms suggestive of asthma and/or allergy, or who were taking any medication for these conditions were clinically examined. All participants were interviewed about respiratory symptoms, and furthermore skin test reactivity, lung function, and airway responsiveness were measured.

A total of 489 individuals had clinical asthma of whom 61% had allergic asthma, whereas 39% had non-allergic asthma. Subjects with non-allergic asthma were more likely to be females, OR = 2.24 (1.32-3.72), p = 0.003, and to have cough as the predominant symptom, OR = 1.96, (1.19-3.23), p = 0.008, but were less likely to have AHR, OR = 0.40, (0.24-0.66), p < 0.001, food allergy, OR = 0.28, (0.11-0.73), p = 0.009, and symptoms of rhinitis, OR = 0.08 (0.05-0.14) compared with subjects with allergic asthma. Subjects with non-allergic asthma had had persistent symptoms within the last 4 weeks more often than subjects with allergic asthma (68% vs. 53%), p = 0.001.

Non-allergic asthma accounts for two in every five cases of asthma in adults and constitutes symptomatically, and in terms of lung function, a more severe form of disease than allergic asthma.