title: Limits of longitudinal decline for the interpretation of annual changes in FEV1 in individuals.
abstract: OBJECTIVE
  Spirometry-based screening programmes often conduct annual assessment of longitudinal changes in forced expiratory volume in 1 second (FEV1) to identify individuals with excessive rates of decline. Both the American Thoracic Society (ATS) and the American College of Occupational and Environmental Medicine (ACOEM) recommend a reference limit value of > or =15% for excessive annual decline. Neither the ATS nor the ACOEM adjust this limit for the precision of the existing spirometry data. The authors propose an improved method of defining the reference limit of longitudinal annual FEV1 decline (LLD) based on the precision of the spirometry data.
  
  
  METHODS
  The authors used data from four monitoring programmes and measured their data precision using a pair-wise within-person variation statistic. They then derived programme- 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 for annual decline was more practical than the absolute limit as it adjusted for gender differences in the magnitude of FEV1. The programme-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 can be generalised to different gender and population groups. A relative limit of approximately 10% appears appropriate for good quality workplace monitoring programmes, 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.
authors.affiliation: Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WV 26505, USA. ehnizdo@cdc.gov
authors.forename: Eva
authors.initials: E
authors.lastname: Hnizdo
authors.forename: Kanta
authors.initials: K
authors.lastname: Sircar
authors.forename: Tieliang
authors.initials: T
authors.lastname: Yan
authors.forename: Philip
authors.initials: P
authors.lastname: Harber
authors.forename: James
authors.initials: J
authors.lastname: Fleming
authors.forename: Henry W
authors.initials: HW
authors.lastname: Glindmeyer
mesh_terms: D000328:Adult; D001249:Asthma / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology; D016535:Bronchial Hyperreactivity / Q000175:diagnosis / Q000453:epidemiology; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology; D009786:Occupational Health Services / Q000379:methods; D012016:Reference Values; D015203:Reproducibility of Results; D012140:Respiratory Tract Diseases / Q000175:diagnosis* / Q000453:epidemiology* / Q000503:physiopathology; D017678:Sex Distribution; D013147:Spirometry / Q000592:standards; D014481:United States / Q000453:epidemiology