Discriminating Measures and Normal Values for Expiratory Obstruction: Recommendation
There are several possible limitations in this study. Although the spirometric measurements followed ATS guidelines, it is possible that some subjects gave incomplete historical details. While we do not have data for Asian individuals or other ethnic groups, the similarity of FEV1/FVC and FEV3/FVC values among thousands of white, black, and Latin adults in the United States, who differed considerably in height and nutritional status, suggests that the values given in Table 4 are likely to be universally valid. In clinical practice, we would express uncertainty when spirometric findings are equivocal, but purposely did not do so in this study. Rather, we distinguished normalcy from abnormality on purely statistical grounds, as have other authors.- The use of a single-tailed LLN at the 95% confidence level in a healthy population causes approximately 5% of each measurement to be “abnormal,” although the subject may not really be abnormal.
Therefore, testing four parameters in 3,570 healthy subjects at the 5% level should result in approximately 714 abnormal values (3,570 X 0.05 X 4 = 714). Lung restriction cannot be diagnosed definitively in this series in the absence of measurements that were not available on the NHANES III database, although Dykstra et al, assessing patients with FEV1/FVC values of < 70%, found a relatively low incidence of reduced total lung capacity. Left ventricular failure with cardiomegaly can result in abnormal spirometry with combined restrictive and obstructive pattern. Thus, significant heart or other diseases, unknown to surveyors, might have been present. read
Although the FEV6 has been suggested as a substitute for the FVC, the FVC often exceeds the FEV6, especially with older age and smoking. Therefore, our analysis does not include FEV1/FEV6 or FEV3/FEV6 values. We did not investigate the role of the duration or intensity of cigarette smoking on spirometric values.
We recommend that manufacturers replace the reporting of spirometric values as “a percent of predicted” with “mean predicted, and lower limit of normal.” In addition, thoracic societies should consider the elimination of FEF25-75 and other forced expiratory flow values from reports, and their replacement with simpler, more valid, and easier to interpret FEV3/FVC values.
Table 4—Approximate FEV1/FVC and FEV3/FVC for All Adults
Age, yr | FEV1/FVC, % | FEV3/FVC, % | ||
Mean | LLN | Mean | LLN | |
Men | ||||
20 | 84.5 | 74.5 | 97.4 | 92.0 |
30 | 82.5 | 72.5 | 95.6 | 90.3 |
40 | 80.6 | 70.6 | 93.8 | 88.5 |
50 | 78.6 | 68.6 | 92.1 | 86.8 |
60 | 76.7 | 66.7 | 90.3 | 85.0 |
70 | 74.7 | 64.7 | 88.6 | 83.3 |
80 | 72.8 | 62.7 | 86.8 | 81.5 |
Women | ||||
20 | 87.1 | 76.9 | 98.3 | 92.5 |
30 | 84.8 | 74.7 | 96.5 | 90.7 |
40 | 82.6 | 72.4 | 94.7 | 88.9 |
50 | 80.3 | 70.2 | 92.9 | 87.1 |
60 | 78.1 | 67.9 | 91.1 | 85.3 |
70 | 75.8 | 65.7 | 89.4 | 83.6 |
80 | 73.6 | 63.5 | 87.6 | 81.8 |