The Effect of a Post-Bronchodilator FEV1/FVC < 0.7 on COPD Diagnosis and Treatment: A Regression Discontinuity Design

Background Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines recommend the diagnosis of chronic obstructive pulmonary disease (COPD) only in patients with a post-bronchodilator forced expiratory volume in 1 second to forced vital capacity ratio (FEV1/FVC) less than 0.7. However the impact of this recommendation on clinical practice is unknown. Research Question What is the effect of a documented post-bronchodilator FEV1/FVC < 0.7 on the diagnosis and treatment of COPD? Study Design and Methods We used a national electronic health record database to identify clinical encounters be- tween 2007 to 2022 with patients 18 years of age and older in which a post-bronchodilator FEV₁/FVC value was documented. An encounter was associated with a COPD diagnosis if a diagnostic code for COPD was assigned, and was associated with COPD treatment if a prescription for a medication commonly used to treat COPD was filled within 90 days. We used a regression discontinuity design to measure the effect of a post-bronchodilator FEV₁/FVC < 0.7 on COPD diagnosis and treatment. Results Among 27 817 clinical encounters, involving 18 991 patients, a post-bronchodilator FEV₁/FVC < 0.7 was present in 14 876 (53.4%). The presence of a documented post-bronchodilator FEV₁/FVC < 0.7 had a small effect on the probability of a COPD diagnosis, increasing by 26.0% (95% confidence interval [CI] 1.1% to 10.9%) from 38.0% just above the 0.7 cutoff to 44.0% just below this cutoff. The presence of a documented post-bronchodilator FEV₁/FVC had no effect on the probability of COPD treatment (−2.1%, 95% CI −7.2% to 3.0%). Interpretation The presence of a documented post-bronchodilator FEV₁/FVC < 0.7 has only a small effect on the probability that a clinician will make a guideline-concordant diagnosis of COPD and has no effect on corresponding treatment decisions.