Cut-off value of FEV₁/FEV₆ to determine airflow limitation using handheld spirometry in subjects with risk of chronic obstructive pulmonary disease

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Korean J Intern Med. 2021;36(3):629-635

Publication date (electronic) : 2020 June 24

doi : https://doi.org/10.3904/kjim.2019.314

Yong Il Hwang^1,2,*, Youlim Kim^2,3,*, Chin Kook Rhee⁴, Deog Kyeom Kim⁵, Yong Bum Park⁶, Kwang Ha Yoo⁷, Ki-Suck Jung^1,2, Chang Youl Lee^2,3

¹Department of Pulmonary, Allergy and Critical Care Medicine, Hallym University Sacred Heart Hospital, Anyang, Korea

²Lung Research Institute of Hallym University College of Medicine, Chuncheon, Korea

³Department of Pulmonary, Allergy and Critical Care Medicine, Hallym University Chuncheon Sacred Heart Hospital, Chuncheon, Korea

⁴Department of Pulmonary, Allergy and Critical Care Medicine, Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea

⁵Department of Pulmonary, Allergy and Critical Care Medicine, Seoul Metropolitan Government Seoul National University Boramae Medical Center, Seoul, Korea

⁶Department of Pulmonary, Allergy and Critical Care Medicine, Hallym University Kangdong Sacred Heart Hospital, Seoul, Korea

⁷Department of Pulmonary, Allergy and Critical Care Medicine, Konkuk University Medical Center, Seoul, Korea

Correspondence to Chang Youl Lee, M.D. Division of Pulmonary, Allergy and Critical Care Medicine, Hallym University Chuncheon Sacred Heart Hospital, 77 Sakju-ro, Chuncheon 24253, Korea Tel: +82-33-240-5482 Fax: +82-33-255-4291 E-mail: doclcy@hallym.or.kr

^*

These authors contributed equally to this work.

Received 2019 September 19; Revised 2019 December 24; Accepted 2020 February 27.

Abstract

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality. It is predicted to become the fourth leading cause of death worldwide by 2030 [1]. Its prevalence and mortality will increase over time and its direct and indirect socio-economic burden will be extremely high [2].

To treat COPD properly, early diagnosis is important to prevent deterioration of pulmonary function and improve treatment outcomes. Pulmonary function tests using conventional spirometry are required to diagnose airflow limitation of COPD. The ratio of forced expiratory volume in 1 second (FEV₁) and forced vital capacity (FVC) needs to be measured in order to calculate whether postbronchodilator FEV₁/FVC is equal to or less than 0.7 as an indicator of airflow limitation [3-5]. However, conventional spirometry is not easy to execute [4,5], because FVC can not be easily measured. In addition, it causes discomfort to patients. Moreover, the result is difficult to reproduce. Thus, COPD is well known to be underdiagnosed in primary care setting [4].

Forced expiratory volume in 6 seconds (FEV₆) has been recently suggested as an alternative to FVC to detect airflow limitation [6,7]. In many patients who have difficult with exhalation, measuring FEV₆ could shorten expiratory time and reduce patients’ discomfort during examination [8]. Several researches have suggested that cut-off values of FEV₁/FEV₆ with conventional spirometry are between 0.7 and 0.8 [9,10]. Handheld spirometry can measure both FEV₁ and FEV₆ simultaneously. Recent active case-finding studies for COPD have shown the effectiveness of handheld spirometry in detecting airflow limitation [9-11]. Therefore, the aim of this study was to find the appropriate cut-off value of FEV₁/FEV₆ to diagnose COPD using handheld spirometry.

METHODS

RESULTS

Study population

A total of 290 subjects participated in this study. Their mean age was 63.1 years. Their mean smoking history was 31.6 pack-years. Proportions of participants who complained of cough, sputum, and dyspnea were 21.0%, 31.0%, and 39.0%, respectively (Table 1). For conventional spirometry with bronchodilator, mean FEV₁ and FEV₁/FVC with a bronchodilator were 82.4% ± 21.1% of the predicted value and 67.5% ± 14.4%, respectively (Table 1). FEV₁/FEV₆ for handheld spirometry and postbronchodilator FEV₁/FVC for conventional spirometry well correlated with each other (r = 0.901, p < 0.001) (Fig. 1).

Table 1.

Baseline characteristics of study participants (n = 290)

Figure 1.

Correlation analysis between forced expiratory volume in 1 second (FEV₁)/forced expiratory volume in 6 seconds (FEV₆) for handheld spirometry and postbronchodilator FEV₁/FVC for conventional spirometry.

ROC curve for handheld spirometry

Using postbronchodilator FEV₁/FVC < 0.7 as a definition of airflow limitation by conventional spirometry, three values (FEV₁/FEV₆ ≤ 73%, FEV₁/FEV₆ ≤ 74%, and FEV₁/FEV₆ ≤ 77%) were compared against each other. FEV₁/FEV₆ ≤ 73% by handheld spirometry had the best sum of sensitivity (86.7%), specificity (89.7%), PPV (88%), and NPV (88.5%) according to the ROC curve analysis for patients diagnosed with COPD. The area under the ROC curve was 0.93 (95% confidence interval [CI], 0.895 to 0.957; p < 0.001) (Table 2, Fig 2).

Table 2.

Sensitivity and specificity of cut-off point of FEV₁/FEV₆ from spirometry

Figure 2.

Receiver-operating characteristic (ROC) curve of forced expiratory volume in 1 second (FEV₁)/forced expiratory volume in 6 seconds (FEV₆) ratio for diagnosing the postbronchodilator FEV₁/FVC < 0.7. AUC, area under the curve; CI, confidence interval.

Comparison according to COPD-6 findings with cut-off value of 73% of FEV₁/FEV₆

A total of 139 participants (47.9%) were found to have COPD by conventional spirometry. Among them, 21 patients (15.1%) had FEV₁/FEV₆ > 73% and 118 (84.9%) had FEV₁/FEV₆ ≤ 73% (Table 3). Patients with abnormal FEV₁/FEV₆ value showed poor lung function significantly in terms of prebronchodilator FEV₁, postbronchodilator FEV₁, and postbronchodilator FEV₁/FVC (Table 3). Differences in age, smoking amount, or respiratory symptoms were not significant between the two groups.

Table 3.

Comparison of COPD patients according to the handheld spirometry with cut-off value of FEV₁/FEV₆ ≤ 0.73^a

DISCUSSION

In this study, we tried to find out the best cut-off value of FEV₁/FEV₆ for diagnosing COPD. With both results of handheld spirometry and conventional spirometry from patients having the risk of COPD, FEV₁/FEV₆ less than or equal to 0.73 was found to be the best cut-off value to detect airflow limitation. It had high sensitivity and specificity. Furthermore, correlation analysis was performed between FEV₁/FEV₆ by handheld spirometry and postbronchodilator FEV₁/FVC by conventional spirometry. The correlation coefficient was 0.901, showing strong positive correlation between the two.

COPD is a preventable and treatable disease when it is diagnosed and treated early. However, a considerable number of patients might be undiagnosed [14]. One of the reasons is that it is difficult to perform conventional spirometry as a diagnostic tool in primary clinics [4,5]. In Korea, only 19.4% of primary care physicians used spirometry with bronchodilator test to assess COPD patients in 2008 [15]. Unfortunately, this figure did not improve much so far. In recent COPD Clinical Appropriateness Report in Korea, spirometry performance rates in primary clinics were still low, ranging from 37.8% to 42.4% [5]. The main reason for not using the spirometer frequently was the difficulty in performing the test [16]. The obstacle of performing conventional spirometry came from measuring FVC. Thus, FEV₆ was suggested as an alternative to FVC. In fact, in previous studies, FEV₁/FEV₆ and FEV₁/FVC showed good agreement, proving that FEV₁/FEV₆ could be a substitute of FEV₁/FVC for detecting airflow limitation. However, these studies were conducted using conventional spirometry [6,7,16].

The most noteworthy aspect of our study was that we analyzed the best value of FEV₁/FEV₆ using handheld spirometry and that it could detect airflow limitation of COPD as a diagnostic value. There have been studies about the best FEV₁/FEV₆ value on the use of handheld spirometry to assess subjects at risk for COPD. One cross-sectional study enrolled patients aged 50 years or older who were current smoker or ex-smoker (at least 1 pack-year) and defined the cut-off value to be 0.73 [10]. Another multicenter study recruited patients with high-risk COPD and set the cut-off point for the FEV₁/FEV₆ ratio < 0.70 with COPD-6 device as prescreening modality of COPD [11]. Although both studies have been conducted to explore active case-finding for COPD with the optimal FEV₁/FEV₆ value, they used FEV₁/FEV₆ value obtained from handheld spirometry as a screening purpose [10,11]. On the other hand, our study enrolled participants aged 40 years or older with risk factors for COPD who had respiratory symptoms and more than 10 pack-years of smoking history and found a cut-off value of 0.73 for FEV₁/FEV₆ with handheld spirometry for diagnosis.

This study has some limitations. First, this study was conducted in a population of patients at risk of COPD, and the cut-off value of FEV₁/FEV₆ < 0.73 obtained in this study was intended to be a guideline for primary care physicians. In recent COPD Clinical Appropriateness Report in Korea [5], spirometry performance rates in primary care clinics just range from 37.8% to 42.4%. We suggest that the cut-off value we proposed in this study can be helpful in diagnosing and treating COPD patients through COPD-6 device, which is more easily available to primary care physicians who have difficulty in using conventional spirometry. However, even though we considered the value from the previous studies, there was no result from the random population. Therefore, it is also necessary to obtain the validity of our values by collecting nation-wide data in the future. Second, the rate of COPD patients in this study was 47.9%, which was higher than that in other studies [16]. Participants of this study were patients who visited a tertiary hospital directly or were referred from primary clinics with high risk of COPD. Thus, the COPD rate was higher than that in the general population. Third, in our study, of 139 patients diagnosed as COPD with conventional spirometry, approximately 15.1% of patients had FEV₁/FEV₆ > 0.73 and reported as normal by handheld spirometry. Patients measured with FEV₁/FEV₆ > 0.73 had higher predicted FEV₁ values in both prebronchodilator (84.4% ± 17.3%) and postbronchodilator (86.5% ± 17.5%) results. They also had higher postbronchodilator FEV₁/FVC than those with FEV₁/FEV₆ ≤ 0.73 (86.5 ± 17.5 vs. 53.8 ± 11.4, p < 0.001). Patients with FEV₁/FEV₆ > 0.73 have relatively good lung function. They may not be treated immediately. Additionally, according to updated GOLD guideline [17], the value between 0.6 and 0.8 for postbronchodilator FEV₁/FVC might change as a biological variation. Indeed, in a study of two large cohorts [18], diagnostic reversal was observed in some patients with mild to moderate airflow limitation. However, less than 0.6 of postbronchodilator FEV₁/FVC at a single measurement would rarely rise to be above 0.7 [17,19]. For these reasons, patients with FEV₁/FEV₆ > 0.73 should be routinely followed up with handheld spirometry. Fourth, we did not show the gender data. Because there was no gender difference in conducting the study, it was not necessary to distinguish it.

In conclusion, our study indicates that the best cut-off value of FEV₁/FEV₆ using handheld spirometry to detect airflow limitation would be 73% or less in subjects with COPD risk factors. Further studies are needed to validate this cut-off value.

KEY MESSAGE

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