Abstract

BackgroundA significant proportion of patients with chronic obstructive pulmonary disease (COPD) remain undiagnosed. Characterising these patients can increase our understanding of the hidden burden of COPD and the effectiveness of case detection interventions.\n\nMethodsWe conducted a systematic review and meta-analysis to compare patient and disease risk factors between patients with undiagnosed persistent airflow limitation and those with diagnosed COPD. We searched MEDLINE and EMBASE for observational studies of adult patients meeting accepted spirometric definitions of COPD. We extracted and pooled summary data on the proportion or mean of each risk factor among diagnosed and undiagnosed patients (unadjusted analysis), and coefficients for the adjusted association between risk factors and diagnosis status (adjusted analysis). This protocol is registered with PROSPERO (CRD42017058235).\n\nFindings2,083 records were identified through database searching and 16 articles were used in the meta-analyses. Diagnosed patients were less likely to have mild (v. moderate to very severe) COPD (odds ratio [OR] 0{middle dot}30, 95% CI 0{middle dot}24-0{middle dot}37, 6 studies) in unadjusted analysis. This association remained significant but its strength was attenuated in the adjusted analysis (OR 0{middle dot}72, 95% CI 0{middle dot}58-0{middle dot}89, 2 studies). Diagnosed patients were more likely to report respiratory symptoms such as wheezing (OR 3{middle dot}51, 95% CI 2{middle dot}19-5{middle dot}63, 3 studies) and phlegm (OR 2{middle dot}16, 95% CI 1{middle dot}38-3{middle dot}38, 3 studies), had more severe dyspnoea (modified Medical Research Council scale mean difference 0{middle dot}52, 95% CI 0{middle dot}40-0{middle dot}64, 3 studies) and slightly greater smoking history than undiagnosed patients. Patient age, sex, current smoking status, and the presence of coughing were not associated with a previous diagnosis.\n\nInterpretationPatients with undiagnosed persistent airflow limitation had less severe airflow obstruction and fewer respiratory symptoms than diagnosed patients. This indicates that there is lower disease burden among undiagnosed patients compared to those with diagnosed COPD, which may significantly delay the diagnosis of COPD.\n\nFundingCanadian Institutes of Health Research.\n\nDeclaration of interestsWe declare no competing interests.\n\nAuthor ContributionsMS, SB, and KJ formulated the study idea and designed the study. KJ and SG performed all data analyses and MS, SB and DS contributed to interpretation of findings. KJ wrote the first draft of the manuscript. All authors critically commented on the manuscript and approved the final version. MS is the guarantor of the manuscript.