Lung function abnormalities in Singapore: a population-based cohort study on preserved ratio impaired spirometry and undiagnosed airway disease

INTRODUCTION: Data on lung function abnormalities in Singapore are limited. Preserved ratio impaired spirometry (PRISm) and undiagnosed obstructive airway disease (UAD) are frequently overlooked conditions associated with worsened respiratory symptoms, airflow obstruction, and higher morbidity and mortality. We aimed to investigate lung function abnormalities in Singapore, including the prevalence, severity and associated factors of PRISm and UAD. METHODS: Participants from the Singapore Population Health Studies were invited to complete a self-administered questionnaire before undergoing health screenings, including spirometry. PRISm is defined as forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ≥ 0.70, with FEV1 < 80% predicted, subcategorised into restrictive (FVC < 80% predicted) and non-restrictive (FVC ≥ 80% predicted). Obstructive airway disease (OAD) is defined as FEV1/FVC < 0.7, subcategorised into UAD and known OAD (KAD) based on prior diagnosis of asthma or chronic obstructive pulmonary disease. RESULTS: Of 2044 participants, 1817 (88.9%) had valid spirometry results. PRISm was present in 294 (16.2%; 14.0% restrictive, 2.2% non-restrictive), and OAD in 100 (5.5%; 3.1% UAD, 2.4% KAD). PRISm was associated with higher body mass index (BMI), Indian ethnicity, hypertension and childhood asthma. Undiagnosed obstructive airway disease was linked to lower BMI, older age, male gender, Malay ethnicity, and current smoking, with milder airflow obstruction than KAD. CONCLUSION: This study highlights the high prevalence and clinical importance of PRISm and UAD in Singapore. Addressing these undiagnosed conditions improves spirometry practices, raise awareness and facilitate early diagnosis. Further research in Southeast Asia is needed to gain deeper insights.