Abstract
BACKGROUND: Spirometry is essential to identify cases with obstructive lung diseases (OLDs) in primary care. However, knowledge about the long-term prognostic outcome among younger individuals is sparse. AIM: To describe the predictive value of spirometry among individuals in the age groups 30-49 years and 45-64 years. DESIGN & SETTING: A population-based cohort study supplied with data from Danish national registries. METHOD: Spirometry was performed in 905 adults aged 30-49 years in 1991 and in 1277 adults aged 45-64 years in 2006. The participants were categorised into three groups: forced expiratory volume in 1 second (FEV(1))/forced vital capacity (FVC) <70, 70-75, and >75. They were followed throughout 2017 using Danish national registries. Lung disease was defined as fulfilling at least one of the following: two prescriptions for respiratory medicine were redeemed within a year; one lung-related contact to the hospital; or lung-related death. RESULTS: In the 1991 cohort, 21% developed lung diseases and in the 2006 cohort 17% developed lung diseases throughout 2017. The probability of developing lung disease if FEV(1)/FVC 70-75 was 35% (95% confidence interval [CI] = 25% to 44%) in the 1991 cohort and 23% (95% CI = 17% to 28%) in the 2006 cohort. The positive predicted value (PPV) was higher for both cohorts when focusing on smoking history and self-reported respiratory symptoms. CONCLUSION: The initial spirometry has a high predictive value to identify cases of future lung diseases. In addition, the group with FEV(1)/FVC 70-75 had a high risk of developing lung diseases later in life, suggesting this group would be a meaningful target of special interest.