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

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. 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 &lt; 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. 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, <i>p</i> &lt; 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 <i>p</i> = 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, <i>p</i> = 0.008). 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.