Research in context
Evidence before this study
We searched PubMed without language restrictions for epidemiological and clinical studies published between Jan 1, 2000, and Sept 15, 2017, using the search terms “COPD”, “follow-up studies”, “diagnosis”, “mortality”, “prognosis”, “survival analysis”, “severity of illness index”, “GOLD classification”, “GOLD 2007”, “GOLD 2011”, “GOLD 2017”, and “prediction”. Searches were supplemented by review of the reference lists of the identified articles. Earlier Global Initiative for Chronic Obstructive Lung Disease (GOLD) classifications were based on either FEV1 thresholds (GOLD 2007) or a combination of spirometry, history of exacerbations, and symptoms (GOLD 2011). The GOLD 2017 classification is based on a composite of spirometry and symptoms or exacerbations and separates the spirometric 1–4 staging from the ABCD groups defined by symptoms and exacerbations. Previous studies have shown that the GOLD 2011 classification does not improve mortality prediction in patients with chronic obstructive pulmonary disease (COPD) compared with the GOLD 2007 classification. We identified only one study comparing mortality for all three GOLD classification systems in our search of the literature. That study included only 524 patients with COPD and did not assess predictive accuracies. We identified no previous large-scale studies examining how well the new GOLD 2017 classification predicts all-cause and respiratory mortality in patients with COPD.
Added value of this study
We prospectively enrolled a cohort of 33 765 patients with COPD with data in the Danish registry for COPD. All patients had attended hospital outpatient clinics in Denmark. We categorised each patient according to the ABCD groups in the GOLD 2017 classification. We further subcategorised by spirometry 1–4 staging, resulting in 16 subgroups (1A to 4D). After adjustment for confounders, we found that 3 year all-cause and respiratory mortality increased from group A to group D. All-cause and respiratory mortality were higher in group B than in group C. Cardiovascular disease-related mortality was high in group B and was similar to cardiovascular disease-related mortality in group D. Receiver operating curve analyses showed that the GOLD 2017 classification based on symptoms and exacerbation risk (ABCD groups) only did not predict all-cause and respiratory mortality more accurately than the older classification systems (GOLD 2007 and 2011). When spirometry results were added to the GOLD 2017 ABCD groups and 16 subgroups were created, we found that 3 year mortality increased successively from subgroup 1A (all-cause mortality 5·4%) to subgroup 4D (all-cause mortality 42·5%) and that the 16 subgroups predicted all-cause and respiratory mortality more accurately than either of the previous GOLD classification systems.
Implications of all the available evidence
This cohort study is the first large-scale study to show that the new GOLD 2017 classification does not predict all-cause and respiratory mortality more accurately than the older GOLD systems, unless the spirometric stages 1–4 and ABCD groups based on symptoms and exacerbations are combined into 16 subgroups.