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

BACKGROUND: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.