Background
The effect of non-obstructive chronic bronchitis (CB) on mortality is unclear.
Research question
Is non-obstructive chronic bronchitis (CB) associated with increased all-cause mortality?
Study design and methods
We performed a systematic literature review and meta-analysis to evaluate the association of non-obstructive BC and all-cause mortality.
PubMed and EMBASE were searched for articles that included both BC and mortality in the title, abstract, or both. Studies in which participants demonstrated obstructive spirometry findings and studies in which BC and mortality were not defined were excluded .
We used the Newcastle-Ottawa Quality Assessment Scale to assess study quality. Adjusted hazard ratios (HRs) were pooled using the random effects model and inverse variance weighting.
We performed an analysis stratified by definition of BC and smoking status. We used Cochrane’s Q and I 2 to assess heterogeneity. Publication bias was assessed by visual inspection of a funnel plot .
Results
Of 5,014 titles identified, eight met the inclusion and exclusion criteria. Overall, nonobstructive BC was associated with all-cause mortality (HR, 1.37; 95% CI, 1.26-1.50) without statistically significant heterogeneity (P = 0.14; I 2 = 29%).
Nonobstructive BC was associated with higher mortality in studies that defined BC as any respiratory symptom (broad definition; HR, 1.28; 95% CI, 1.10-1.48; I 2 = 0%), as well as in the rest of the studies (HR, 1.40; 95% CI, 1.26-1.56; I 2 = 37%).
Nonobstructive BC was associated with increased mortality in smokers (HR, 1.49; 95% CI, 1.35-1.64; I 2 = 0%), but was not associated with increased mortality in never smokers (HR, 1.22; 95% CI, 0.90-1.66), and moderate heterogeneity was found (p = 0.10; I 2 = 49%).
The funnel plot did not indicate evidence of publication bias because it showed a symmetrical distribution of studies.
Interpretation
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