Minimum Clinically Important Difference in Diffusing Capacity of the Lungs for Carbon Monoxide Among Patients with Severe and Very Severe Chronic Obstructive Pulmonary Disease

Background: The minimum clinically important difference (MCID) for diffusing capacity of the lungs for carbon monoxide (DLCO) has not yet been solidly established. Methods: We used the dataset of surgical cohort of National Emphysema Treatment Trial. Briefly, severe and very severe chronic obstructive pulmonary disease (COPD) patients who were candidate for volume reduction surgery and who could provide sufficient data at 12-month follow-up were included. We used two anchor methods using 6-minute walk distance (6MWD. MCID = 40 m) and forced expiratory volume in 1 sec (FEV1. MCID = 100 ml) as anchors, and two distribution methods. We proposed MCID with a median of estimated values. We estimated MCID for DLCO in raw value and % change from the baseline independently. Results: The surgical cohort included 356 patients, whose average age was 66.6 +/- 5.5 years, and the average % predicted FEV 1 was 27.8 +/- 7.3%. The estimated MCID for DLCO in raw value and % change from the baseline were as follows: anchor method (average, 6MWD) 1.2 ml/min/mmHg, 17%; anchor method (average, FEV1) 0.7 ml/min/mmHg, 11%; anchor method (receiver operating characteristic, 6MWD) 1.1 ml/min/mmHg, 10%; anchor method (receiver operating characteristic, FEV1) 1.2 ml/min/mmHg, 3%; distribution method (0.3 units of standard deviation), 0.9 ml/min/mmHg, 11%; distribution method (standard error of measurement), 1.1 ml/min/mmHg. The median of these values was 1.1 ml/min/mmHg and 11%. Conclusion: We estimated the group-level MCID for DLCO for patients with severe and very severe COPD patients as 1.1 ml/min/mmHg and 11% of baseline DLCO.