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doi:10.1378/chest.06-1349
(Chest. 2007; 131:349-355)
© 2007 American College of Chest Physicians
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Spirometric Criteria for Airway Obstruction*

Use Percentage of FEV1/FVC Ratio Below the Fifth Percentile, Not < 70%

James E. Hansen, MD, FCCP; Xing-Guo Sun, MD and Karlman Wasserman, PhD, MD, FCCP

* From the Division of Respiratory and Critical Care Physiology and Medicine, Department of Medicine, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA.

Correspondence to: James E. Hansen, MD, FCCP, Box 405, Harbor-UCLA Medical Center, Torrance, CA 90509; e-mail: jhansen{at}labiomed.org

Abstract

Background: Current authoritative spirometry guidelines use conflicting percentage of FEV1/FVC ratios (FEV1/FVC%) to define airway obstruction. The American Thoracic Society/European Respiratory Society Task Force characterizes obstruction as a FEV1/FVC% below the statistically defined fifth percentile of normal. However, many recent publications continue to use the Global Initiative for Chronic Obstructive Lung Disease (GOLD) primary criterion that defines obstruction as a FEV1/FVC% < 70%. Data from the Third National Health and Nutrition Examination Survey (NHANES-III) should identify and quantify differences, help resolve this conflict, and reduce inappropriate medical and public health decisions resulting from misidentification.

Methods: Using these two guidelines, individual values of FEV1/FVC% were compared by decades in 5,906 healthy never-smoking adults and 3,497 current-smokers of black (African American), Hispanic (Latin), or white ethnicities aged 20.0 to 79.9 years.

Results: In the never-smoking population, the lower limits of normal used in other reference equations fit reasonably well the NHANES-III statistically defined fifth percentile guidelines. But nearly one half of young adults with FEV1/FVC% below the NHANES-III fifth percentile of normal were misidentified as normal because their FEV1/FVC% was > 70% (abnormals misidentified as normal). Approximately one fifth of older adults with observed FEV1/FVC% above the NHANES-III fifth percentile had FEV1/FVC% ratios < 70% (normals misidentified as abnormal).

Conclusions: The GOLD guidelines misidentify nearly one half of abnormal younger adults as normal and misidentify approximately one fifth of normal older adults as abnormal.

Key Words: airway obstruction • percentage of predicted FEV1/FVC • reference values • spirometry

In 1966, Sobol and Weinheimer1 pointed out the error of using fixed percentages of spirometric predicted values to define abnormality. In 1988, Miller and Pincock2 emphasized the necessity of using statistically derived lower limits of normal (LLN). Currently, however, respected organizations of pulmonary specialists have defined spirometric airway obstruction in conflicting ways, resulting in ongoing confusion regarding the prevalence of airway obstruction in a general or specific population. The most recent guideline of the American Thoracic Society (ATS)/European Respiratory Society (ERS) Task Force interpretative strategies,3 with which the authors agree, states that an "obstructive ventilatory defect ... is defined as a reduced forced expiratory volume in one second/vital capacity ratio (FEV1/VC) below the fifth percentile of the predicted value." This definition contrasts with that described by the Global Initiative for Chronic Obstructive Lung Disease (GOLD),4 and reinforced in the most current GOLD guidelines5 and the 2004 ATS/ERS standards for diagnosis and treatment of patients with COPD, as summarized in their position statement.6 These latter publications primarily define airway obstruction as percentage of FEV1/FVC (FEV1/FVC%) < 70%, even though it is recognized that this fixed ratio identifies an unusually high incidence of obstruction in older never-smoking individuals unexposed to noxious particles or gases.7 Despite this recognition and its lack of statistical justification, many current reports8910111213 continue to use the fixed limit of FEV1/FVC% < 70% to identify and define airway obstruction, a usage that tends to underestimate airway obstruction in the young and overestimate it in older adults. Minor considerations are as follows: (1) the ratio denominator should be FVC or vital capacity (VC), since the latter is often larger in those with airway obstruction14; (2) spirometric values after aerosolized bronchodilators are necessary4; and (3) a reduction in FEV1 is necessary to diagnose airflow obstruction. To further explore the potential magnitude of the problem and importance of selecting good criteria of airflow obstruction, the authors used high-quality spirometric data from nearly 10,000 ethnically defined, healthy never-smokers and current-smokers in the United States15 to quantify the degree of overidentification and underidentification of airway obstruction as related to age.

Materials and Methods

Subjects
Subjects were 5,906 never-smoking adults without recognized respiratory or musculoskeletal disease and 3,497 current-smoking adults from the Third National Health and Nutrition Examination Survey (NHANES-III) database16 from ages 20.0 to 79.9 years (third to eighth decades). Each subject selected (Table 1 ) was classified ethnically as black, Latin, or white, and had performed repeated spirometric maneuvers meeting ATS standards.1516 These data from unidentified subjects had been ethically obtained with informed consent and Institutional Review Board approval.


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  		Table 1. Number of NHANES-III Subjects Included in Study

 
Analysis and Statistics
First, Hankinson et al17 LLN equations for FEV1/FVC% specific for sex, ethnicity, and age, and derived from healthy NHANES-III never-smokers were used. By decade, sex, and ethnicity, the 9,403 individual subjects in each never-smoking and current-smoking group were identified as being above or below the fifth percentile of normal. If above, such individuals were identified as normal; if below, they were considered to have a < 5% chance of being normal and were therefore identified as abnormal.18 Second, by decade, sex, and ethnicity, the individual subjects in each never-smoking and current-smoking group who had FEV1/FVC% < 70% were similarly identified.

Third, by sex and smoking status, grouping all ethnicities together, we identified the number and percentage of subjects in each decade with the following characteristics: (1) obstruction as per both guidelines (both abnormal [BA]); (2) normal by both guidelines (both normal [BN]); (3) below the fifth percentile but with FEV1/FVC% ratio ≥ 70% (false negative [FN]); or (4) above or equal to the fifth percentile but FEV1/FVC% ratio < 70% (false positive [FP]). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for each decade by gender and smoking status (Table 2 ).


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  		Table 2. Summary of Abbreviations and Formulae Used

 
Fourth, considering the Hankinson et al17 fifth percentile as the "correct" and "gold standard," we calculated for each decade and smoking status the normal and abnormal subjects misidentified by substituting the FEV1/FVC% < 70% or ≥ 70% standard: abnormals misidentified as normals, FN/(FN +BA), ie, 1 – sensitivity; and normals misidentified as abnormals, FP/(FP + BN), ie, 1 – specificity. Fifth, to further assess the validity of the formulae used by Hankinson et al,17 we compared two other frequently used American FEV1/FVC% formulae1920 for never-smokers with well-defined fifth percentile limits to see if the number per decade of the "abnormal" 2,189 white never-smoking individuals from the NHANES-III database16 approximated 5%.

Results

The percentage of NHANES-III never-smokers with FEV1/FVC% < 70% are shown by decade of age, sex, and ethnicity in Figure 1 , top, A. For each group, the prevalence was < 5% for the third and fourth decades; thereafter, it increased to 6 to 14% for the sixth decade, 11 to 18% for the seventh decade, and 19 to 33% for the eighth decade. If ethnic- and sex-specific groups were weighted equally, mean values for the third through eighth decades, respectively, were 2.0%, 2.6%, 4.7%, 8.3%, 14.6%, and 25.3%. These values contrast with an optimal 5% during each decade. Figure 1, bottom, B, shows similar values for the current-smoking population. With equal weighting, mean values for the third through eighth decades, respectively, were 3.2%, 5.1%, 14.1%, 31.9%, 42.2%, and 54.4%. For 11 of the 12 group/decade comparisons, the percentages for men exceeded those of women, likely because men normally have lower FEV1/FVC% values than women of the same age.


Figure 1
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  		Figure 1. Percentages of healthy 5,906 NHANES-III never-smokers (top, A) and 3,497 current-smokers (bottom, B), by sex, ethnicity, and decade, with observed FEV1/FVC% < 70%. Observed FEV1/FVC% < 70%, rather than the statistically valid fifth percentile, is the primary GOLD spirometric criterion used to screen for airway obstruction. Among never-smokers, all of those above the expected fifth percentile dashed line will be improperly identified as "airway obstruction" using the GOLD FEV1/FVC% < 70% criterion. Among current-smokers, some of those above the expected fifth percentile dashed line will be improperly identified as "airway obstruction" using the GOLD FEV1/FVC% < 70% criterion.

 
Table 3 gives details of the third analysis. Sensitivities were low in all groups in the third and fourth decades, so that overall sensitivity from 20 to 39.9 years is only 41% (bottom of Table 3). After the fifth decade, the percentages of FN cases are negligible, but FP-observed FEV1/FVC% values continue to increase. For the seventh and eighth decades, specificity (correct diagnosis of nonobstruction) has declined from 100 to 81% while the PPV (percentage of reliability of positive test results) has declined from 100 to 55%.


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  		Table 3. Comparison of Observed FEV1/FVC% < 70% or Greater Than or Equal to the Fifth Percentile LLN with Observed FEV1/FVC% < 70% or ≥ 70%*

 
Figure 2 shows the results of the fourth analysis, in which abnormals were misidentified, FN/(FN + BA), and normals were misidentified, FP/(FP + BN), using data from Table 3. More than one half of those in the third and fourth decades and one fifth in the fifth decade with an observed FEV1/FVC% below the fifth percentile for their age were wrongly identified (abnormals misidentified) as not having airway obstruction because their observed FEV1/FVC% was ≥ 70%. Further, approximately one fourth of current-smokers and one eighth of never-smokers in the seventh and eighth decades who had observed FEV1/FVC% above the fifth percentile were wrongly identified (normals misidentified) as having airway obstruction because their observed FEV1/FVC% was < 70%. Thus, the standard of FEV1/FVC% < 70% or ≥ 70% underidentifies airway obstruction in the younger adults, and overidentifies airway obstruction in older adults. Table 4 shows that, for each decade, approximately 5% of the NHANES-III never-smokers had observed FEV1/FVC% values below the fifth percentile, whether the Hankinson et al,17 Crapo et al,19 or Knudson et al20 reference equations were used.


Figure 2
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  		Figure 2. Underidentification and overidentification of airway obstruction, by decade, in 5,906 never-smokers and 3,497 current-smokers using the GOLD 70% of FEV1/FVC% as a criterion. For each decade, the left of the paired columns are never-smokers (N-S) and the right of the paired columns are current smokers (C-S). The columns below the zero line are abnormals misidentified as normals; the columns above zero line are normals misidentified as abnormals. This criterion causes underidentification of airway obstruction in the younger subjects, reasonable identification in early middle age, and overidentification in the older subjects.

 

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  		Table 4. NHANES-III Never-Smoking White Adults With FEV1/FVC% Below the Fifth Percentile LLN Using Three Sets of Reference Values*

 
Discussion

This study illustrates the importance of using statistically valid spirometric criteria to identify the prevalence of airway obstruction. Use of the GOLD criterion to identify obstruction as an FEV1/FVC% < 70% results in finding an inappropriately high prevalence of obstruction in adults in seventh and eighth decades, among never-smokers and probably among current-smokers. Confirmatory evidences in these decades are the relatively low specificity and very low PPV (Table 3) and high ratios of normals misidentified as abnormals (Fig 2). The latter indicate that approximately one seventh of never-smokers and one fifth of current-smokers in these decades with FEV1/FVC% above the fifth percentile LLN would be misidentified as having airway obstruction using the GOLD FEV1/FVC% criterion (Fig 2).

Also importantly, the observed GOLD FEV1/FVC% criterion fails to identify airway obstruction in many in the third to fifth decades of life. Confirming this finding are the 19 to 46% sensitivity in the third decade and the 32 to 64% sensitivity in the fourth decade (Table 3), plus the high frequency of misidentified normal subjects (approximately two thirds in the third decade, one half in the fourth decade, and one fifth in the fifth decade (Fig 2). The latter indicates that in these decades, nearly half of those with observed FEV1/FVC% values below fifth percentile LLN values would not be considered to have airway obstruction by the GOLD criterion because their observed FEV1/FVC% ≥ 70%.

The continuing use of the GOLD 70% criterion, with inherent lowered sensitivity, specificity, and PPV, seems both unfortunate and unnecessary. We do not question the numeric value of the observed FEV1/FVC%, only an interpretation based on a fixed standard for all adults.

The 2005 ATS/ERS definition of airway obstruction,3 ie, a FEV1/FVC% below the fifth percentile of a normal never-smoking population of similar age, is statistically valid. In cross-sectional studies, although the FEV1 begins to decline earlier than the FVC with increasing age in never-smoking populations after maturity,17 decline in FEV1/FVC% appears to be quite linear within each gender and ethnic group, at least in survivors to age 70 or 80 years.17202122 Confirmatory is the finding in three commonly used reference groups that approximately 5% of healthy never-smoking adults have FEV1/FVC% below the 95% confidence limits.

The high percentage of older never- and current-smoking adults with observed FEV1/FVC% < 70% noted in Figure 1 deserves comment. Clearly, many of these individuals have FEV1/FVC% that are well within normal limits for their age and should not be identified or treated as having airways obstruction. As also found, many current-smoking adults in their third and fourth decades with FEV1/FVC% below the LLN should not be dismissed as normal because their FEV1/FVC% is > 70% (Fig 2).

Spirometric surveys do not identify the specific cause of airway obstruction or the presence or absence of disease. Nevertheless, spirometry can help identify lung injury due to exposure to occupational hazards, tobacco smoke, and other noxious inhalants. Clinical findings including history, physical examination, response to inhaled bronchodilators, and measurement of gas transfer index are useful in recognizing if airway obstruction may be due to asthma, chronic bronchitis, emphysema, acute or chronic infection, or acute or chronic inhalant exposure. Using poor spirometric criteria may lead to misdirection of resources, unnecessary costs, and individual and societal harm. The planning for and necessity of preventative or therapeutic interventions and their cost/benefit ratio should be based on the best available spirometric criteria.

GOLD defends its definition of airway obstruction as an FEV1/FVC% < 70% on the basis of its simplicity and ease of remembrance.4 To the authors, these reasons seem unimportant compared to the objective of being able to properly detect airway obstruction in the young or prevent the overdiagnosis and treatment of older individuals who do not have airway obstruction. For example, in this era, the use of the body mass index to define obesity is not discarded because the formula uses the square of height. The additional GOLD criterion4 requiring a reduction in the absolute value of FEV1 to identify airway obstruction can be questioned because in three commonly used reference groups,171920 coefficients of variation for volume measures such as FEV1 and FVC for a given age, gender, and height are approximately 1.5 to 3 times those for the FEV1/FVC ratio. However, the GOLD criterion4 that concerns response to bronchodilators should be helpful in differential diagnosis, but the prebronchodilator spirometric values are key in identifying whether or not baseline airway obstruction is present.

Following are some examples in which use of GOLD criteria could lead to ill-advised actions. Lundback et al,8 Wilson et al,23 and Celli et al al13 correctly noted that the prevalence of airway obstruction in their studies depended on what spirometric criteria were used, yet they failed to advocate using fifth percentile values. Kim et al,12 on the basis of FEV1/FVC% <70%, concluded that 26% of Korean men and 10% of Korean women > 45 years old have COPD. Of those > 45 years, 20% of men and 91% of women were never-smokers. Behrendt,11 using the NHANES-III data for 7,526 never-smokers and a cut-off for FEV1/FVC% of 70%, concluded that 16 to 18% of those never-smokers aged 60 to 69 years and 25 to 30% of those aged 70 to 79 years had COPD. The high prevalence in both latter studies1112 is undoubtedly due to not using appropriate age-specific fifth percentile values.

Normal aging changes should not be considered disease or abnormal. Other examples of aging-related physiologic changes in which age is factored into predicted values are peak heart rate, peak oxygen uptake, VC, and FEV1. As previously noted, the primary measurement of airway obstruction, FEV1/FVC% declines linearly with age, at least in American and European never-smoking populations.171920212224 Only when these normal declines are exceeded should the spirometric finding of airway obstruction be made. Because of the variability of spirometric values within the general population, minimized by reference to age, height, sex, and ethnicity, values below fifth percentile have been recommended for use in identifying abnormality since 1991.25 Of the several measurements advocated to identify airway obstruction, the FEV1/FVC%, the percentage of forced expiratory volume in 3 s/FVC, and percentage of predicted FEV1/forced expiratory volume in 6 s (FEV1/FEV6%), all ratios of volume/volume, have lower coefficients of variation than those of individual lung volumes1719202224 and much lower coefficients of variation than measures of flow dependent on volume, such as forced expiratory flow, mid-expiratory range, or forced expiratory flow at 50% of VC.171920 A proper concern is whether the FVC alone, without obtaining the slow or unforced VC for expressing the percentage of FEV1/VC, suffices as a denominator in ascertaining the presence of airway obstruction.14 In the our experience, when evaluating a general population, the VC and FVC are usually quite similar; but with moderate-to-severe obstructive disease, the VC may be considerably larger, strengthening the evidence of airway obstruction.

The FEV1/FEV6% has been proposed as a substitute for the FEV1/FVC% in screening for airway obstruction.26 Although the FEV1/FEV6% ratio may suffice adequately in patients with known significant airway obstruction,272829 it seems to discriminate airway obstruction less well in a general population.30

A recent suggestion to use mean values of FEV1/FVC% minus 1 SD to identify airway obstruction23 seems unwise, since approximately an additional 15% of normal never-smokers would be identified with airway obstruction using this criterion. In conclusion, we recommend that the GOLD criterion of airway obstruction as an observed FEV1/FVC% < 70% be discarded. Its usage causes significant underidentification of airway obstruction in the young and overidentification in older individuals and populations.

Footnotes

Abbreviations: ATS = American Thoracic Society; BA = both abnormal; BN = both normal; ERS = European Respiratory Society; FEV1/FEV6% = percentage of FEV1/forced expiratory volume in 6 s; FEV1/FVC% = percentage of FEV1/FVC; FN = false negative; FP = false positive; GOLD = Global Initiative for Chronic Obstructive Lung Disease; LLN = lower limit/limits of normal; NHANES-III = Third National Health and Nutritional Examination Survey; NPV = negative predictive value; PPV = positive predictive value; VC = vital capacity

Support was provided by the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center.

There is no financial support or author involvement with organizations with financial interest in the subject matter.

Received for publication May 30, 2006. Accepted for publication September 20, 2006.

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