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Conflicting Definitions of Airways Obstruction: Drawing the Line Between Normal and Abnormal

Mary C. Townsend, DrPH
Author and Funding Information

Affiliations: Pittsburgh, PA ,  Dr. Townsend is principal/consultant, M. C. Townsend Associates, LLC, and adjunct assistant professor, University of Pittsburgh Graduate School of Public Health, Departments of Epidemiology and Environmental and Occupational Health.

Correspondence to: Mary C. Townsend, DrPH, M.C. Townsend Associates, 289 Park Entrance Dr, Pittsburgh, PA 15228; e-mail: mary.townsend4@verizon.net



Chest. 2007;131(2):335-336. doi:10.1378/chest.06-2736
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Although the pulmonary community has generally agreed over time on what constitutes serious airways obstruction, there has been disagreement over the past 40 years on where the line should be drawn to separate normal from abnormal. Traditional clinical practice has relied on fixed cut-off points, such as 80% of the predicted value, to distinguish normal from abnormal results.1 But since the mid-1960s, clinicians and researchers have noted that the distributions of the primary spirometric measurements, FEV1 and FVC, are homoscedastic with age, so that normal healthy pulmonary function measures are likely to remain in a roughly fixed position relative to their predicted values as the subject ages.6 For the past 15 years, the American Thoracic Society (ATS) official spirometry interpretation statements have discouraged the use of fixed spirometry cut-off points to define abnormality because normal individuals will drift below those fixed points with age, even if the subjects are not symptomatic or exposed to known respiratory hazards.

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