Repeated measures of FEV1 over six to twelve months: what change is abnormal?

Monitoring change in FEV1 (deltaFEV1) is useful for assessing adverse respiratory effects in an individual, but high variability impedes reliable recognition of accelerated decline. The American Thoracic Society (ATS) recommends a > or =15% year-to-year FEV1 decline for clinical significance. To evaluate the applicability of this criterion in health monitoring programs, we examined the mean, lower 5th percentile, and lower 5% cutoff value of deltaFEV1 determined from 2 tests at 6- and 12-month intervals using data obtained with ATS-recommended equipment and procedures in 389 white male workers, each with 3 to 11 spirometry tests over 5 years. Results indicate that when healthy working males perform spirometry according to ATS standards, a yearly decline in FEV1 greater than 8% or 330 mL should not be considered normal, whereas the 15% ATS criterion could be appropriate in clinical settings.