title: A simplified score to quantify comorbidity in COPD.
abstract: OBJECTIVE
  Comorbidities are common in COPD, but quantifying their burden is difficult. Currently there is a COPD-specific comorbidity index to predict mortality and another to predict general quality of life. We sought to develop and validate a COPD-specific comorbidity score that reflects comorbidity burden on patient-centered outcomes.
  
  
  METHODS
  Using the COPDGene study (GOLD II-IV COPD), we developed comorbidity scores to describe patient-centered outcomes employing three techniques: 1) simple count, 2) weighted score, and 3) weighted score based upon statistical selection procedure. We tested associations, area under the Curve (AUC) and calibration statistics to validate scores internally with outcomes of respiratory disease-specific quality of life (St. George's Respiratory Questionnaire, SGRQ), six minute walk distance (6MWD), modified Medical Research Council (mMRC) dyspnea score and exacerbation risk, ultimately choosing one score for external validation in SPIROMICS.
  
  
  RESULTS
  Associations between comorbidities and all outcomes were comparable across the three scores. All scores added predictive ability to models including age, gender, race, current smoking status, pack-years smoked and FEV1 (p<0.001 for all comparisons). Area under the curve (AUC) was similar between all three scores across outcomes: SGRQ (range 0·7624-0·7676), MMRC (0·7590-0·7644), 6MWD (0·7531-0·7560) and exacerbation risk (0·6831-0·6919). Because of similar performance, the comorbidity count was used for external validation. In the SPIROMICS cohort, the comorbidity count performed well to predict SGRQ (AUC 0·7891), MMRC (AUC 0·7611), 6MWD (AUC 0·7086), and exacerbation risk (AUC 0·7341).
  
  
  CONCLUSIONS
  Quantifying comorbidity provides a more thorough understanding of the risk for patient-centered outcomes in COPD. A comorbidity count performs well to quantify comorbidity in a diverse population with COPD.
authors.affiliation: Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Nirupama
authors.initials: N
authors.lastname: Putcha
authors.affiliation: Epidemiology, Biostatistics & Prevention Institute, University of Zurich, Zurich, Switzerland.
authors.forename: Milo A
authors.initials: MA
authors.lastname: Puhan
authors.affiliation: Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: M Bradley
authors.initials: MB
authors.lastname: Drummond
authors.affiliation: Pulmonary & Critical Care Medicine, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: MeiLan K
authors.initials: MK
authors.lastname: Han
authors.affiliation: Department of Medicine, National Jewish Health, Denver, Colorado, United States of America.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Regan
authors.affiliation: Pulmonary, Critical Care and Sleep Medicine, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Nicola A
authors.initials: NA
authors.lastname: Hanania
authors.affiliation: Pulmonary & Critical Care Medicine, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: Carlos H
authors.initials: CH
authors.lastname: Martinez
authors.affiliation: Pulmonary and Critical Care Medicine, Morehouse School of Medicine, Atlanta, Georgia, United States of America.
authors.forename: Marilyn
authors.initials: M
authors.lastname: Foreman
authors.affiliation: Pulmonary, Allergy and Critical Care Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States of America.
authors.forename: Surya P
authors.initials: SP
authors.lastname: Bhatt
authors.affiliation: Pulmonary and Critical Care, National Jewish Health, Denver, Colorado, United States of America.
authors.forename: Barry
authors.initials: B
authors.lastname: Make
authors.affiliation: Pulmonary and Critical Care Medicine, University of California San Diego, San Diego, California, United States of America.
authors.forename: Joe
authors.initials: J
authors.lastname: Ramsdell
authors.affiliation: Channing Division of Network Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Dawn L
authors.initials: DL
authors.lastname: DeMeo
authors.affiliation: Department of Medicine, Department of Epidemiology, Columbia University Medical Center, New York City, New York, United States of America.
authors.forename: R Graham
authors.initials: RG
authors.lastname: Barr
authors.affiliation: Pulmonary and Critical Care Medicine, University of Nebraska Medical Center, Omaha, Nebraska, United States of America.
authors.forename: Stephen I
authors.initials: SI
authors.lastname: Rennard
authors.affiliation: Pulmonary and Critical Care Medicine, New York Presbyterian-Weill Cornell Medical College, New York City, New York, United States of America.
authors.forename: Fernando
authors.initials: F
authors.lastname: Martinez
authors.affiliation: Channing Division of Network Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Edwin K
authors.initials: EK
authors.lastname: Silverman
authors.affiliation: Pulmonary and Critical Care, National Jewish Health, Denver, Colorado, United States of America.
authors.forename: James
authors.initials: J
authors.lastname: Crapo
authors.affiliation: Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Wise
authors.affiliation: Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Nadia N
authors.initials: NN
authors.lastname: Hansel
mesh_terms: D019540:Area Under Curve; D015897:Comorbidity; D017281:Cost of Illness; D006305:Health Status Indicators; D006801:Humans; D063868:Patient Outcome Assessment; D029424:Pulmonary Disease, Chronic Obstructive / Q000453:epidemiology*; D011788:Quality of Life; D011795:Surveys and Questionnaires