Effect of change of reference standard to NHANES III on interpretation of spirometric ‘abnormality’

Abstract

The American Thoracic Society has recently recommended the use of NHANES III spirometric reference standard in the United States. The objective of this study was to better quantify the well-known ‘problem’ of the change in interpretation of spirometry, as a consequence of the change from the other commonly used reference standards (Morris, Kory, Crapo, Knudson 1976, and Knudson 1983) to NHANES III. This is a cross-sectional study of spirometries of 1,106 non-Hispanic Caucasian American adults, including 234 subjects with obstructive and 228 subjects with restrictive spirometric ‘abnormalities’. A weighted Kappa statistic was used to evaluate the level of agreement between NHANES III and other commonly used reference standards. The level of agreement in assessing the presence of an ‘abnormality’ was poor to moderate – values of Kappa statistic ranged from 0.13 to 0.46. There was however, good to very good level of agreement in assessing the severity of the ‘abnormality’ – values of Kappa statistic ranged from 0.61 to 0.91. This study better quantifies the well-known differences in the interpretation of spirometric ‘abnormalities’ as a consequence of the recommended change of reference standard to NHANES III, which in turn may cause confusion among patients and their treating physicians.

Keywords:

• Reference standard
• Classification of severity
• Obstructive spirometric abnormality’
• Restrictive spirometric ‘abnormality’
• Kappa statistic

Acknowledgements

The authors would like to thank William S. Beckett, M.D., M.P.H., Professor of Medicine and Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY, and Mark Schuyler, M.D., Professor of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM, for their careful review and editorial changes.

Institution at which the work was performed: Southern Illinois University School of Medicine, Springfield, IL

Grant support: University of New Mexico General Clinical Research Center grant number M01-RR-00997 (AS, CQ)

Conflict of interest

None of the authors have any conflict of interest, including any financial conflict of interest (such as employment, consultancy, stock ownership, honoraria and paid expert testimony) as well as other forms of conflict of interest, including personal, academic and intellectual issues.