Introduction: Underdiagnosis and misclassification of COPD jeopardize adequate healthcare. An understanding of the magnitude and associated characteristics is important.

Aim: To investigate the occurrence of and factors associated with underdiagnosis and misclassification of COPD.

Method: Individuals with COPD_GOLD (post-bronchodilator FEV₁/FVC<0.70 + respiratory symptoms) were identified among 1839 participants in two large-scale epidemiological research programs; the Obstructive Lung Disease in Northern Sweden Studies and the West Sweden Asthma Study.

Results: Among the 128 participants fulfilling the criteria for COPD_GOLD, 21 reported a physician-diagnosed COPD corresponding to an underdiagnosis of 83.6%. The 107 underdiagnosed participants were mainly males (57.9%) and never smokers, had a lower mean age and higher FEV1% of predicted than diagnosed. Underdiagnosis was unrelated to socioeconomic status. One in four of the underdiagnosed participants, had utilized healthcare and/or emergency care due to respiratory symptoms. Six were misclassified, i.e. reported a physician-diagnosed COPD without fulfilling the criteria for COPD_GOLD. They were mainly ex-smoking females, had low education, respiratory symptoms or an asthma diagnosis.

Conclusion: Underdiagnosis of COPD was high, although a fairly high proportion had utilized healthcare because of respiratory symptoms. Misclassification was lower than previously reported. Increased adherence to diagnostic recommendations and case-finding strategies based on characteristics associated with underdiagnosis is suggested as early recognition of COPD is vital to initiate patient education and treatment to prevent exacerbations and improve health status.