Study objective: Spirometry is performed to monitor lung health, but variability between tests can hinder recognition of excessive FEV1 declines. We sought to describe the relationship between FEV1 changes over 1 to 5 years and FEV1 declines over longer terms, using 21,821 test results from 1,884 workers who participated in an annual health monitoring program at a chemical plant between 1973 and 2003.
Methods: Test results from workers with five or more valid results over ≥ 10 years were included in our analysis (mean initial worker age, 35 years; range, 18 to 62 years; 91% male; 35% current smokers and 41% nonsmokers). For each worker, long-term FEV1 slopes (milliliters per year) were calculated by simple linear regression using all available results and compared to changes in FEV1 between two tests over 1 to 5 years, expressed in both milliliters and percentage of initial value.
Results: Long-term (mean, 18 years; range, 10 to 30 years) slopes averaged − 29.1 mL/yr (− 27, − 29, and − 37 mL/yr for male never-smokers, former smokers, and current smokers, and − 20, − 26, and − 27 mL/yr for female never-smokers, former smokers, and current smokers, respectively). Excessive short-term and long-term declines were defined by lower fifth percentile values. Individuals with abnormal short-term declines were found to be 3 to 18 times more likely to ultimately show excessive long-term declines; with the strength of the association increasing with the length of the short-term testing interval. Better test operating characteristics resulted if abnormal short-term FEV1 change was based on percentage change (ie, percentage per year) rather than absolute change (ie, milliliters per year).
Conclusions: Our findings provide guidance for interpreting periodic spirometry results from individuals exposed to respiratory hazards.