Rationale: Chronic obstructive pulmonary disease (COPD) is a chronic, progressive disease, and reversal of COPD diagnosis is thought to be uncommon.
Objectives: To determine whether a spirometric diagnosis of mild or moderate COPD is subject to variability and potential error.
Methods: We examined two prospective cohort studies that enrolled subjects with mild to moderate post-bronchodilator airflow obstruction. The Lung Health Study (n = 5,861 subjects; study duration, 5 yr) and the Canadian Cohort of Obstructive Lung Disease (CanCOLD) study (n = 1,551 subjects; study duration, 4 yr) were examined to determine frequencies of (1) diagnostic instability, represented by how often patients initially met criteria for a spirometric diagnosis of COPD but then crossed the diagnostic threshold to normal and then crossed back to COPD over a series of annual visits, or vice versa; and (2) diagnostic reversals, defined as how often an individual's COPD diagnosis at the study outset reversed to normal by the end of the study.
Measurements and Main Results: Diagnostic instability was common and occurred in 19.5% of the Lung Health Study subjects and 6.4% of the CanCOLD subjects. Diagnostic reversals of COPD from the beginning to the end of the study period occurred in 12.6% and 27.2% of subjects in the Lung Health Study and CanCOLD study, respectively. The risk of diagnostic instability was greatest for subjects whose baseline FEV1/FVC value was closest to the diagnostic threshold, and the risk of diagnostic reversal was greatest for subjects who quit smoking during the study.
Conclusions: A single post-bronchodilator spirometric assessment may not be reliable for diagnosing COPD in patients with mild to moderate airflow obstruction at baseline.