The effect of a post-bronchodilator FEV1/FVC < 0.7 on COPD diagnosis and treatment: a regression discontinuity design

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 s to forced vital capacity ratio (FEV1/FVC) less than 0.7. However the impact of this recommendation on clinical practice is unknown. To estimate the effect of a documented post-bronchodilator FEV1/FVC < 0.7 on the diagnosis and treatment of COPD. We used a regression discontinuity design to measure the effect of a post-bronchodilator FEV1/FVC < 0.7 on COPD diagnosis and treatment. Patients included in a national electronic health record database who were 18 years of age and older and had a clinical encounter between 2007 and 2022 in which a post-bronchodilator FEV1/FVC value was documented. An encounter was associated with a COPD diagnosis if an international classification of disease 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. 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 increased the probability of a COPD diagnosis by 6.0% (95% confidence interval CI 1.1–10.9%) 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 < 0.7 had no effect on the probability of COPD treatment (−2.1%, 95% CI −7.2 to 3.0%). The presence of a documented post-bronchodilator FEV1/FVC < 0.7 had only a small effect on the diagnosis of COPD and no effect on corresponding treatment decisions.