Risk Factors Associated with Irreversible Airway Obstruction in Asthma: A Systematic Review and Meta-Analysis.

Irreversible airway obstruction (IAO) is a subtype of asthma and relates to poorer prognosis in some asthma patients. However, the prevalence and risk factors for IAO are unknown. A systematic review regarding controlled clinical studies (cohort, case-control studies) on IAO asthma in adult and/or children affected by asthma/early wheeze was performed. Eighteen papers were identified in this study. It was reported that the incidence of IAO at random effects or fixed effects in severe asthma and nonsevere asthma was 0.54 (95% CI: 0.45-0.62) and 0.16 (95% CI: 0.12-0.20), respectively. In IAO asthma, the pooled odds ratio (OR) related to smoking exposure was 2.22 (95% CI: 1.82-2.73), the OR for male, smoking, and fractional exhaled nitric oxide (FENO) was 2.22 (95% CI: 1.82-2.7), 1.79 (95% CI: 1.46-2.19), and 2.16 (95% CI: 1.05-4.43), respectively, suggesting these factors increase the risk of IAO. However, a decreased OR in IAO asthma was observed due to rhinitis (OR = 0.31, 95% CI: 0.24-0.40), atopy (OR = 0.584, 95% CI: 0.466-0.732), and atopic dermatitis (OR = 0.60, 95% CI: 0.42-0.85), indicating these factors are associated with reduced risk of IAO. IAO in asthma is associated with gender, smoking, FENO, rhinitis, atopy, and atopic dermatitis.