Occup Environ Med 64:701-707 doi:10.1136/oem.2006.031146
  • Original article

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

  1. Eva Hnizdo1,
  2. Kanta Sircar1,
  3. Tieliang Yan2,
  4. Philip Harber3,
  5. James Fleming4,
  6. Henry W Glindmeyer5
  1. 1
    Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WV, USA
  2. 2
    Constella Group, Morgantown, WV, USA
  3. 3
    Division of Occupational and Environmental Medicine, Department of Family Medicine, University of California Los Angeles, Los Angeles, CA, USA
  4. 4
    Phoenix Fire Department, Phoenix, AZ, USA
  5. 5
    Section of Pulmonary, Critical Care, and Environmental Medicine, Department of Medicine, Tulane Medical School, New Orleans, LA, USA
  1. Dr E Hnizdo, Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA; ehnizdo{at}
  • Accepted 20 April 2007
  • Published Online First 3 May 2007


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 ⩾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.

Method: 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.


  • Competing interests: None declared.

  • Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.

  • Abbreviations:
    American College of Occupational and Environmental Medicine
    American Thoracic Society
    bronchial hyper-reactivity
    chronic obstructive pulmonary disease
    European Respiratory Society
    forced expiratory volume in 1 second
    limit of longitudinal decline
    lower limit of normal
    National Institute for Occupational Safety and Health

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