J Korean Med Sci.  2024 Jan;39(4):e20. 10.3346/jkms.2024.39.e20.

Spirometric Interpretation and Clinical Relevance According to Different Reference Equations

• Lee HW
• Lee JK
• Hwang YI
• Seo H
• Ahn JH
• Kim SR
• Kim HJ
• Jung KS
• Yoo KH
• Kim DK

• KMID: 2551963
• DOI: http://doi.org/10.3346/jkms.2024.39.e20

Abstract

Background
Global Lung Function Initiative (GLI)-2012 reference equation is currently suggested for interpretation of spirometry results and a new local reference equation has been developed in South Korea. However, lung function profiles according to the different reference equations and their clinical relevance have not been identified in chronic obstructive pulmonary disease (COPD) patients.
Methods
Our cross-sectional study evaluated Choi’s, Korean National Health and National Examination Survey (KNHANES)-VI, and GLI-2012 reference equations. We estimated the percentages of predictive forced expiratory volume in one second (FEV ₁) and airflow limitation severity according to reference equations and analyzed their associations with patient reported outcomes (PROs): COPD assessment test (CAT) score, St. George's Respiratory Questionnaire for COPD patients (SGRQ-C) score, and six minute walk distance (6MWD).
Results
In the eligible 2,180 COPD patients, lower predicted values of FEV ₁ and forced vital capacity (FVC) were found in GLI-2012 compared to Choi's and KNHANES-VI equations. GLI-2012 equation resulted in a lower proportion of patients being classified as FEV ₁ < 80% or FVC < 80% compared to the other equations. However, the Z-scores of FEV ₁ and FVC were similar between the KNHANES-VI and GLI-2012 equations. Three reference equations exhibited significant associations between FEV ₁ (%) and patient-reported outcomes (CAT score, SGRQ-C score, and 6MWD).
Conclusion
GLI-2012 reference equation may not accurately reflect FEV ₁ (%) in the Korean population, but the Z-score using GLI-2012 equation can be a viable option for assessing FEV ₁ and airflow limitation in COPD patients. Similar to the other two equations, the GLI-2012 equation demonstrated significant associations with PROs.

Keyword

Spirometry; Pulmonary Disease; Chronic Obstructive; Reference Values; Forced Expiratory Volume; Patient Reported Outcome Measures

Figure

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  Fig. 1 Association between CAT score and different reference equations of FEV1. The vertical dotted line indicates the optimal cut-off value of FEV1% to predict CAT ≥ 10. R2 was 0.078 (P < 0.001) between CAT score and FEV1% (Choi’s reference equation), and 0.084 (P < 0.001) between CAT score and FEV1% (KNHANES-VI reference equation), and 0.073 (P < 0.001) between CAT score and FEV1% (GLI-2012 reference equation).CAT = COPD assessment test, FEV1 = forced expiratory volume in one second, GOLD = Global Initiative for Chronic Obstructive Lung Disease, KNHANES = Korean National Health and Nutritional Examination Survey, GLI = Global Lung Function Initiative.

• 

  Fig. 2 Association between SGRQ-C score and different reference equations of FEV1. The vertical dotted line indicates the optimal cut-off value of FEV1% to predict SGRQ-C score ≥20. R2 was 0.132 (P < 0.001) between SGRQ-C score and FEV1% (Choi’s reference equation), and 0.145 (P < 0.001) between SGRQ-C score and FEV1% (KNHANES-VI reference equation), and 0.128 (P < 0.001) between SGRQ-C score and FEV1% (GLI-2012 reference equation).SGRQ-C = St. George’s Respiratory Questionnaire for COPD patients, FEV1 = forced expiratory volume in one second, GOLD = Global Initiative for Chronic Obstructive Lung Disease, KNHANES = Korean National Health and Nutritional Examination Survey, GLI = Global Lung Function Initiative.

• 

  Fig. 3 Association between 6MWD and different reference equations of FEV1. The vertical dotted line indicates the optimal cut-off value of FEV1% to predict 6MWD ≥ 400. R2 was 0.033 (P < 0.001) between 6MWD and FEV1% (Choi’s reference equation), and 0.035 (P < 0.001) between 6MWD and FEV1% (KNHANES-VI reference equation), and 0.050 (P < 0.001) between 6MWD and FEV1% (GLI-2012 reference equation).6MWD = 6-minute walking distance, FEV1 = forced expiratory volume in one second, GOLD = Global Initiative for Chronic Obstructive Lung Disease, KNHANES = Korean National Health and Nutritional Examination Survey, GLI = Global Lung Function Initiative.

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