Chest
Volume 130, Issue 1, July 2006, Pages 200-206
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Original Research
FEV1/FVC Ratio of 70% Misclassifies Patients With Obstruction at the Extremes of Age

https://doi.org/10.1378/chest.130.1.200Get rights and content

Background

The American Thoracic Society recommends using the lower limit of normal (LLN) method to diagnose obstructive lung disease. However, few studies have investigated the clinical relevance of these recommendations. We compared the LLN derived from available data sets to a fixed ratio (FEV1/FVC, < 75% or 70%) and also to the FEV1/FVC percent predicted ratio to determine the impact of changing the FEV1/FVC “cutoff” on the spirometric diagnosis of obstructive lung disease.

Methods

FEV1, FVC, FEV1/FVC ratio, age, race, sex, height, and weight were recorded from 1,503 pulmonary function tests. Predicted values were calculated using the Third National Health and Nutrition Examination Study data set (Hankinson), and reference values from studies by Crapo, Knudson, and Morris. In addition, the LLN of the FEV1/FVC ratio was calculated for the Hankinson and Crapo reference values.

Results

The number of studies interpreted as obstructed varied from 37% using the Hankinson data set to 55% using the 75% fixed ratio method. Comparing the LLN method vs the 70% fixed ratio method resulted in 7.5% (Hankinson LLN vs 70% fixed) and 6.9% (Crapo LLN vs 70% fixed), which were discordant results. Age was the strongest predictor of discordance, and 16% of subjects > 74 years of age had discordant results comparing Hankinson values to the 70% fixed method.

Conclusion

At the extremes of age and height, a large number of spirometry test results will be interpreted as showing an obstructive defect if a 70% fixed ratio method is used for interpretation compared with the LLN derived from the Hankinson data set.

Section snippets

Materials and Methods

Consecutive spirometry tests from three hospitals at two academic medical centers between December 1, 2003, and February 29, 2004, were reviewed. Results were taken from the University Hospital at The Ohio State University, and from Indiana University Hospital and Wishard Memorial Hospital, both of which were a part of the Indiana University Medical Center. All PFTs were performed and reported with the goal of meeting ATS standards for acceptability and reproducibility.11 Tests were reviewed,

Results

A total of 1,503 PFT results were collected and analyzed from the 3-month period. A total of 1,003 were from The Ohio State University Medical Center and 500 from the Indiana University Medical Center (Wishard Memorial Hospital, 248 PFT results; Indiana University Medical Center, 252 PFT results). Table 1shows the distribution of subjects.

The percentage of PFT results that were classified as obstruction varied markedly based on which method of diagnosis was used (ranging from 55% of patients

Discussion

The ATS recommends12 using a statistically based method for the determination of LLN, and the newest ATS guidelines2 recommend the use of the Hankinson data set as the data set to be used in the US population. The National Lung Health Education Program recommends that primary care practitioners use the data set of the Third National Health and Nutrition Examination Study (the Hankinson data set) and define the LLN for the purposes of diagnosis of obstruction in screening office spirometry.9

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The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

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