COPD classification models and mortality prediction capacity

Abstract

Objective

Our aim was to assess the impact of comorbidities on existing COPD prognosis scores.

Patients and methods

A total of 543 patients with COPD (FEV₁ <80% and FEV₁/FVC <70%) were included between January 2003 and January 2004. Patients were stable for at least 6 weeks before inclusion and were followed for 5 years without any intervention by the research team. Comorbidities and causes of death were established from medical reports or information from primary care medical records. The GOLD system and the body mass index, obstruction, dyspnea and exercise (BODE) index were used for COPD classification. Patients were also classified into four clusters depending on the respiratory disease and comorbidities. Cluster analysis was performed by combining multiple correspondence analyses and automatic classification. Receiver operating characteristic curves and the area under the curve (AUC) were calculated for each model, and the DeLong test was used to evaluate differences between AUCs. Improvement in prediction ability was analyzed by the DeLong test, category-free net reclassification improvement and the integrated discrimination index.

Results

Among the 543 patients enrolled, 521 (96%) were male, with a mean age of 68 years, mean body mass index 28.3 and mean FEV₁% 55%. A total of 167 patients died during the study follow-up. Comorbidities were prevalent in our cohort, with a mean Charlson index of 2.4. The most prevalent comorbidities were hypertension, diabetes mellitus and cardiovascular diseases. On comparing the BODE index, GOLD_ABCD, GOLD₂₀₁₇ and cluster analysis for predicting mortality, cluster system was found to be superior compared with GOLD₂₀₁₇ (0.654 vs 0.722, P=0.006), without significant differences between other classification models. When cardiovascular comorbidities and chronic renal failure were added to the existing scores, their prognostic capacity was statistically superior (P<0.001).

Conclusion

Comorbidities should be taken into account in COPD management scores due to their prevalence and impact on mortality.

Keywords:

• comorbidities
• COPD
• mortality
• GOLD
• cluster analysis
• BODE index

Acknowledgments

This work was supported by Fondo de Investigación Sanitaria (grant number PI020510), Departamento de Sanidad del Gobierno Vasco (grant number 200111002), and Departamento de Educación, Cultura y Política Lingüística del Gobierno Vasco (grant numbers IT620-13 and Publibeca SEPAR 2016 [the latter grant paid for editing of the manuscript]).

Author contributions

All authors participated in the conception and design of the study. CE, IA and IB supervised the data collection. IA and IB analyzed and interpreted the data. AA wrote the first and all consecutive drafts of the manuscript. CE, JMQ, AGL and AU provided critical contributions to the drafts of the manuscript. All authors contributed to data analysis, drafting and revising the article, gave final approval of the version to be published, and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.