Limits of longitudinal decline for the interpretation of annual changes in FEV1 in individuals

Abstract

Objective: Spirometry based screening programs often conduct annual assessment of longitudinal changes in FEV1 in order to identify individuals with excessive decline. Both the American Thoracic Society (ATS) and the American College of Occupational and Environmental Medicine (ACOEM) recommend a reference limit value of ¡Ý15% for excessive annual decline. Neither ATS nor ACOEM adjust this limit for the precision of the existing spirometry data. We propose an improved method of defining the reference limit of longitudinal annual FEV1 decline (LLD) based on the precision of the spirometry data. Method: We used data from four monitoring programs and measured their data precision using a pair-wise within-person variation statistic. We then derived program- and gender-specific absolute and relative LLD values and validated these against the 95th percentiles for observed yearly changes in FEV1. Results: The relative limit method was more practical than the absolute limit as it adjusted for gender differences in the magnitude of FEV1. The program-specific relative limit values were in good agreement with 95th percentiles for year-to-year FEV1 changes and ranged from 6.6% to 15.8%. For individuals with COPD and bronchial hyperreactivity the 95th percentiles for year-to-year changes were about 15% and higher. Conclusions: The relative longitudinal limit for annual FEV1 decline based upon precision of measurements is valid and generalizable for different gender and population groups. A relative limit of approximately 10% appears appropriate for good quality workplace monitoring programs, whereas a limit of about 15% appears appropriate for clinical evaluation of individuals with an obstructive airway disease. Computer software based on the method described is available from the corresponding author.