Preserved Ratio Impaired Spirometry Is an Important Risk Factor for Development of COPD, Also in Those Who Do Not Smoke.

Background: COPD largely is underdiagnosed. Active identification of cases is crucial to establish preventive measures before manifestation of clinical disease. The significance of different spirometric patterns preceding COPD, especially preserved ratio impaired spirometry (PRISm) findings, has been highlighted but remains unclear.

Research question: Which clinical characteristics, smoking habits, and spirometric patterns, with primary focus on PRISm findings, precede the development of airway obstruction (AO)?

Study design and methods: The OLIN COPD COPD Study was established from 2002 through 2004. After re-examination of population-based cohorts, individuals with AO (n = 993; FEV₁ to VC ratio < 0.70) were identified together with control participants with nonobstructive findings (n = 993; FEV₁ to VC ratio ≥ 0.70). Most of these people had participated in examinations during the 1980s or 1990s, and in total, 902 patients and 819 control participants had previous clinical data. Logistic regression was performed with case status as outcome and spirometric patterns, age, sex, smoking habits, and BMI at first examination as covariates.

Results: The mean (SD) person-years between first examination and inclusion in the OLIN COPD COPD Study was 10.5 (4.0) years. At first examination, the prevalence of PRISm findings was higher in patients (18.6%) vs control participants (13.4%). Current smoking was more common in patients (45.1% vs 18.2%), whereas former smoking was similar (31.8% vs 34.9%). Patients reported more respiratory symptoms (78.0% vs 44.3%) than control participants. At first examination, PRISm findings, current smoking, and former smoking were associated strongly with becoming a case when adjusted for confounders, with adjusted OR (aOR) of 3.5, 4.1, and 1.5, respectively. When stratifying for smoking habits, aORs for PRISm findings in those with current smoking, former smoking, and never smoking status were 2.9, 3.8 and 3.7, respectively.

Interpretation: PRISm findings are associated with transition into AO corresponding to COPD within 1 decade, independent of smoking habits and with similar strength of association among those who have never smoked, who formerly smoked, and who currently smoke.