Interpreting periodic lung function tests in individuals: the relationship between 1- to 5-year and long-term FEV1...

Spirometry is performed to monitor lung health, but variability between tests can hinder recognition of excessive FEV(1) declines. We sought to describe the relationship between FEV(1) changes over 1 to 5 years and FEV(1) 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.

Test results from workers with five or more valid results over > or = 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 FEV(1) slopes (milliliters per year) were calculated by simple linear regression using all available results and compared to changes in FEV(1) between two tests over 1 to 5 years, expressed in both milliliters and percentage of initial value.

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 FEV(1) change was based on percentage change (ie, percentage per year) rather than absolute change (ie, milliliters per year).

Our findings provide guidance for interpreting periodic spirometry results from individuals exposed to respiratory hazards.