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Defining the Lower Limit of Normal for FEV₁/ FVC

We read the recent article by Johannessen and colleagues (1) with interest in that they suggest the lower limit of normal (LLN) for FEV₁ expressed as a percent of FVC (FEV₁%) is above 70% in both sexes regardless of age. This article is now cited by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) (2) as evidence in favor of their adoption of a flat 70% cutoff to define the presence of airflow limitation when making the diagnosis of COPD. There is a major reason to question Johannessen and coworkers' assertion about a 70% limit. The equipment used in the Johannessen study is known to overrecord FEV₁ relative to FVC by about 5% (3, 4). This is due to the fact that the time constant of cooling of the instrument is not instantaneous so that applying the usual BTPS correction to FEV₁ is incorrect and too large. This fact is acknowledged by the manufacturer. Furthermore, the instrument stops its timed recording at 6 seconds.

The exact manner in which FVC was recorded in the study is not clear, but if the subjects were allowed to continue accumulating volume beyond 6 seconds to reach the assumed FVC then end-of-test criteria for FVC (5) could not have been assessed. Thus, FEV₁ will have been overrecorded and FVC may have been underrecorded, which together will falsely raise the derived FEV₁% value. Therefore, we do not think these data can be reliably used to support the view that 70% is a reasonable LLN for FEV₁% for either adult men or women of any age.

Martin R. Miller

University Hospital Birmingham NHS Trust, Birmingham, United Kingdom

Irene Steenbruggen

Isala Klinieken, Zwolle, The Netherlands

Philip H. Quanjer

Leiden University, Leiden, The Netherlands

Gregg Ruppel

St. Louis University Hospital, St.Louis, Missouri

Robert O. Crapo

LDS Hospital, Salt Lake City, Utah

Ole F. Pedersen

Aarhus University, Aarhus, Denmark

FOOTNOTES

Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

REFERENCES

1. Johannessen A, Lehmann S, Omenaas ER, Elder GE, Bakke PS, Gulsvik A. Post-bronchodilator spirometry reference values in adults and implications for disease management. Am J Respir Crit Care Med 2006;173:1316–1325.[Abstract/Free Full Text]
2. Global strategy for the diagnosis, management and prevention of chronic obstructive pulmonary disease [Internet]. Available at: http://www.goldcopd.com (accessed December 20, 2006).
3. Perks WH, Sopwith T, Brown D, Jones CH, Green M. Effects of temperature on Vitalograph spirometer readings. Thorax 1983;38:592–594.[Abstract/Free Full Text]
4. Pincock AC, Miller MR. The effect of temperature on recording spirograms. Am Rev Respir Dis 1983;128:894–898.[Medline]
5. Miller MR, Hankinson J, Brusasco V, Burgos F, Casaburi R, Coates A, Crapo R, Enright P, van der Grinten CPM, Gustafsson P, et al. Standardisation of spirometry. Eur Respir J 2005;26:319–338.[Abstract/Free Full Text]

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