Increased Accuracy After Adjustment of Spirometry Threshold for Diagnosing COPD Based on Pre-Bronchodilator FEV₁/FVC

COPD is a leading cause of morbidity and mortality worldwide. Spirometry is the most common lung function test for diagnosing COPD with a post-bronchodilator FEV₁/FVC < 0.70 confirming the presence of the disease. However, diagnosticians appear reluctant to use bronchodilators, which have been linked to the misdiagnosis of COPD. Therefore, we investigated whether the threshold for diagnosing COPD should be modified when diagnosing COPD based on pre-bronchodilator spirometry.

Data from 23,433 participants were merged from the National Health and Nutrition Examination Survey (NHANES) 2007-2012. Participants were excluded for having no post-bronchodilator spirometry, for being below the age of 40, and for having asthma or lung cancer. These exclusion criteria resulted in 680 participants being included in the present study. Participants with COPD were defined as those with a post-bronchodilator FEV₁/FVC < 0.70. The threshold for diagnosing COPD based on pre-bronchodilator FEV₁/FVC was varied while calculating accuracy, sensitivity, specificity, positive predictive value, and negative predictive value.

Diagnosing COPD based on pre-bronchodilator FEV₁/FVC < 0.70 contributes to the misdiagnosis of COPD through poor classification rates. By adjusting the threshold and diagnosing COPD based on a pre-bronchodilator FEV₁/FVC < 0.66, the overall classification rates increase noticeably, resulting in a 15% increase in accuracy.

We suggest a slight adjustment using pre-bronchodilator FEV₁/FVC < 0.66 when diagnosing COPD based on pre-bronchodilator spirometry. This approach could prevent cases of misdiagnosed COPD, which can lead to potentially harmful treatment of people who do not have COPD and foregone treatment in patients with COPD.