Minimal Important Difference of FEV₁ and FVC in COPD Patients Undergoing Bronchoscopic Lung Volume Reduction

Spirometry is essential for the diagnosis, severity assessment and longitudinal monitoring of Chronic Obstructive Pulmonary Disease (COPD). However, the minimal important difference (MID) for key spirometric parameters such as forced expiratory volume in one second (FEV₁) and forced vital capacity (FVC) remains poorly defined, particularly in patients with severe COPD. This study aimed was to determine the MID for FEV₁ and FVC in patients with severe COPD undergoing bronchoscopic lung volume reduction treatment.

We retrospectively analyzed data from patients with severe COPD who underwent bronchoscopic lung volume reduction between 2009 and 2024 at the University Medical Center Groningen. Anchor-based methods were used to calculate the MID for FEV₁ and FVC using the 6-minute walk distance and St. George's Respiratory Questionnaire (SGRQ) as anchors.

A total of 543 patients with severe COPD were included, predominantly female (68%) with a mean age of 62±8 years and baseline FEV₁ of 27%±8 predicted. Anchor-based analyses yielded MIDs of approximately 139mL (relative: 19%) for FEV₁ and 349mL (16%) for FVC at 6 months, and 127mL (17%) for FEV₁ and 379mL (17%) for FVC at 12 months.

The overall estimated MID for FEV₁ in our population of patients with severe emphysema was 133mL (18%) and for FVC 364mL (16%). While the MID should not be interpreted as a strict cut-off, consensus on its values is essential to facilitate comparability across studies and to guide appropriate sample size calculations. Validation of these estimates in other COPD populations would be valuable.