Novel FEV₁/FVC-based Diagnosis and Severity Classification of Chronic Obstructive Pulmonary Disease: How about FEV₁ % Predicted Basing?

To the Editor:

We read with interest the article by Bhatt and colleagues (1). The authors proposed a new scheme for grading the severity of chronic obstructive pulmonary disease (COPD): STaging of Airflow obstruction by Ratio (STAR), an FEV₁/FVC–based stratification approach (using FEV₁/FVC thresholds of ⩾0.60 to <0.70, ⩾0.50 to <0.60, ⩾0.40 to <0.50, and <0.40, respectively, for stages 1–4). The predictive performance for 10-year mortality of STAR grades was comparable with that of the conventional FEV₁ % predicted (ppFEV₁)–based stratification, Global Initiative for Chronic Obstructive Lung Disease (GOLD) grades (2). Moreover, STAR showed a more uniform gradation of disease severity, as it provided better ability to discriminate survival between mild COPD (stage 1) and non-COPD compared with the GOLD stages.

Recently, several studies have shown the clinical importance of preserved ratio impaired spirometry (PRISm; FEV₁/FVC ⩾ 0.70 and ppFEV₁ < 0.80), especially for its high incidence of COPD and poor prognosis (3, 4). Nonetheless, subjects with PRISm may be often overlooked, as it does not meet the conventional criterion for COPD (FEV₁/FVC < 0.70) (2). Given the rising interest in the epidemiologic issues of PRISm, physicians today may have to investigate the implications of impaired ppFEV₁, including PRISm, together with COPD in clinical research.

In the study by Bhatt and colleagues (1), non-COPD was defined as FEV₁/FVC ⩾ 0.70 regardless the value of ppFEV₁, which is in line with GOLD standards; subjects with PRISm were included in the non-COPD group. According to Figure 1 in Bhatt and colleagues’ paper, ppFEV₁ in subjects without COPD was distributed unfavorably to that in GOLD stage 1 subjects, whereas ppFEV₁ was higher in subjects without COPD than in STAR stage 1. As a decrease in ppFEV₁ has been known to be a strong risk factor for COPD morbidity and mortality (5, 6), the discrepancy in overall survival between STAR stage 1 and GOLD stage 1 was considered sensible to the difference in ppFEV₁ between them. Therefore, to assess the impact of ppFEV₁ on all-cause mortality, it is crucial to stratify the entire cohort regardless of the values of FEV₁/FVC (not only subjects with COPD) according to ppFEV₁ (i.e., ppFEV₁ thresholds of ⩾0.80, ⩾0.50 to <0.80, ⩾0.30 to <0.50, and <0.30) and to assess the mortality of each subgroup. In addition, a comparison of prognostic performance between ppFEV₁ and FEV₁/FVC among all subjects might make physicians reconsider not only the severity grading but also the diagnostic criteria for COPD, as the cutoff points for the diagnosis of other major noncommunicable diseases (e.g., hypertension, diabetes, dyslipidemia) were established on the evidence of morbidity and mortality.

In conclusion, the work by Bhatt and colleagues (1) is intriguing, in that FEV₁/FVC—a simply calculable biomarker without age-, gender-, height-, and race-dependent predicted values—could be helpful in evaluating disease severity as well as diagnosing COPD. We believe that this new STAR can create a STIR in clinical practice and the management of COPD.