Minimal clinically important differences in COPD lung function.

The FEV1 is widely used by physicians in the diagnosis, staging, treatment, monitoring, and establishing prognosis for patients with COPD. The MCID is the smallest difference which patients perceive as beneficial and which would mandate a change in patient management. A precise MCID for FEV1 has not been established. In attempt to establish a MCID for predose or trough FEV1, several limitations need to be addressed. There are issues such as reproducibility, repeatability, acceptability, variability, placebo effect, and equipment effects. Patient factors, such as baseline level of FEV1, albuterol reversibility, diurnal variation, influence the results. Nonetheless, using anchoring techniques, a change in pre dose FEV1 of about 100 mL can be perceived by patients, correlates with fewer relapses following exacerbations and is in the range usually achieved with bronchodilators approved for COPD. In the future, consistent reporting of spirometric variables, such as a predose FEV1 and other outcomes, can be incorporated into a more quantitative effort to establish the MCID. Also distributional/statistical methods may be useful in determining the MCID FEV1.