FEV1/FVC Severity Stages for Chronic Obstructive Pulmonary Disease

Abstract

Rationale: The diagnosis of chronic obstructive pulmonary disease (COPD) is based on a low FEV₁/FVC ratio, but the severity of COPD is classified using FEV₁% predicted (ppFEV₁). Objectives: To test a new severity classification scheme for COPD using FEV₁/FVC ratio, a more robust measure of airflow obstruction than ppFEV₁. Methods: In COPDGene (Genetic Epidemiology of COPD) (N = 10,132), the severity of airflow obstruction was categorized by Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages 1-4 (ppFEV₁ of ⩾80%, ⩾50-80%, ⩾30-50%, and <30%). A new severity classification (STaging of Airflow obstruction by Ratio; STAR) was tested in COPDGene-FEV₁/FVC ⩾0.60 to <0.70, ⩾0.50 to <0.60, ⩾0.40 to <0.50, and <0.40, respectively, for stages 1-4-and applied to the combined Pittsburgh SCCOR and Emphysema COPD Research Registry for replication (N = 2,017). Measurements and Main Results: The agreements (weighted Bangdiwala B values) between GOLD and the new FEV₁/FVC ratio severity stages were 0.89 in COPDGene and 0.88 in the Pittsburgh cohort. In COPDGene and the Pittsburgh cohort, compared with GOLD staging, STAR provided significant discrimination between the absence of airflow obstruction and stage 1 for all-cause mortality, respiratory quality of life, dyspnea, airway wall thickness, exacerbations, and lung function decline. No major differences were noted for emphysema, small airway disease, and 6-minute-walk distance. The STAR classification system identified a greater number of adults with stage 3/4 disease who would be eligible for lung transplantation and lung volume reduction procedure evaluations. Conclusions: The new STAR severity classification scheme provides discrimination for mortality that is similar to the GOLD classification but with a more uniform gradation of disease severity. STAR differentiates patients' symptoms, disease burden, and prognosis better than the existing scheme based on ppFEV₁, and is less sensitive to race/ethnicity and other demographic characteristics.

Keywords: COPD; airflow obstruction; severity; staging.

Figure 1.

Distribution of disease severity by Global Initiative for Chronic Obstructive Lung Disease stage and STaging of Airflow obstruction using Ratio (STAR) severity category in the COPDGene (Genetic Epidemiology of COPD) study. Groups are STAR severity stages. COPD = chronic obstructive pulmonary disease.

Figure 2.

Bangdiwala agreement charts comparing classification of severity of airflow obstruction using the Global Initiative for Chronic Obstructive Lung Disease (GOLD) and STaging of Airflow obstruction using Ratio (STAR) severity scheme in (A) COPDGene and (B) Pittsburgh cohorts. (C) Redistribution of GOLD severity stages by STAR. The agreement plot is displayed as an n × n square, where n is the total sample size. Each large rectangle shows the maximum possible agreement given the marginal totals. Each dark rectangle indicates complete agreement. Successively lighter-shaded rectangles indicate partial agreement. Perfect agreement would be indicated by all groups showing dark perfect squares and a 45° diagonal line touching the edges of each square. The numbers on the top and right axes represent subjects placed in each GOLD and STAR stage, respectively. COPD = chronic obstructive pulmonary disease.

Figure 3.

Kaplan-Meier curves for all-cause mortality by GOLD and STAR stages. COPDGene = Genetic Epidemiology of COPD; GOLD = Global Initiative for Chronic Obstructive Lung Disease; STAR = STaging of Airflow obstruction using Ratio.