Preserved ratio impaired spirometry and mortality in non-smoking asthma: a population-based cohort study.

Background: Preserved ratio impaired spirometry (PRISm) is associated with asthma. However, it is unclear whether PRISm increases the risk of mortality in non-smoking asthma patients compared with normal spirometry.

Methods: This prospective cohort study included 748 adult asthma participants with no smoking history and no airflow obstruction at baseline. Participants were divided into two groups: normal spirometry (FEV₁ ≥ 80% predicted) and PRISm (FEV₁ < 80% predicted). The median follow-up time was 9.6 years. Multivariable Cox regression analyses and Kaplan-Meier survival were used to assess the association between PRISm and all-cause mortality. All analyses took into account the complex survey design.

Results: At baseline, 8.52% of participants exhibited PRISm. Multivariable Cox regression analysis showed that PRISm was independently associated with all-cause mortality after adjusting for confounding factors (adjusted hazard ratio = 6.57, 95% CI: 2.33-18.47, p < 0.001). Kaplan-Meier survival analysis showed that the survival rate in the PRISm group was significantly worse than that in the normal spirometry group (log-rank test p = 0.006). In a sensitivity analysis excluding participants with possible restrictive spirometry, this association remained with almost the same effect size (adjusted hazard ratio = 6.99, 95% CI: 1.67-29.29, p = 0.008).

Conclusions: In asthma patients with no smoking history and no airflow obstruction at baseline, PRISm was significantly associated with an increased risk of all-cause mortality during follow-up. However, this result needs to be interpreted with caution due to the wide confidence intervals.