Seven retrospective cohort studies (89,196 participants, range 733 to 58,270) were included in the review: three published studies and four unpublished reports.
Statistically significant benefits were observed with treatment with inhaled corticosteroids plus LABAs. There were reductions in asthma-related emergency room admissions (OR 0.84, 95% CI 0.76 to 0.94; four studies, 82,996 participants) and asthma-related hospitalisation (OR 0.85, 95% CI 0.74 to 0.97; four studies, 82,996 participants) compared to when inhaled corticosteroids were used alone. There was no evidence of statistically significant heterogeneity across the results for these outcomes. Similar results were found in subgroup and sensitivity analyses.
Significant reductions were observed in asthma exacerbations (OR 0.82, 95% CI 0.72 to 0.94; seven studies, 89,196 participants, Χ²=18.03, p=0.006). Sensitivity analyses conducted on the basis of asthma severity and the exclusion of one particular study from the analysis did not affect the overall findings.