At what FEV1 percentage is COPD classified as severe?

In the classification of Chronic Obstructive Pulmonary Disease (COPD), severity is primarily determined by measuring Forced Expiratory Volume in one second (FEV1) as a percentage of predicted values. According to international guidelines, COPD is classified as severe when the FEV1 is below 40% of the predicted value. This criterion indicates significant airflow limitation, greater respiratory symptoms, and an increased risk of complications, which often necessitates intensified management strategies.

Patients with an FEV1 below 40% typically experience more pronounced respiratory limitations, more frequent exacerbations, and require closer monitoring and potentially more aggressive treatment. Therefore, understanding this classification is crucial in the effective management and prognosis of patients with COPD.