title: Asthma and COPD overlap syndrome is associated with increased risk of hospitalisation.
abstract: BACKGROUND
  Chronic obstructive pulmonary disease (COPD) is associated with poor prognosis and a high health care burden. The incidence of asthma and COPD overlap syndrome is increasing, and contributes to a high financial burden and poor prognosis.
  
  
  OBJECTIVE
  To investigate clinical features of the overlap syndrome among Asian patients and to analyse its impact on hospitalisation due to respiratory problems or death compared to COPD alone.
  
  
  METHODS
  We performed a retrospective cohort analysis of 2933 COPD patients presenting at the Asan Medical Center from 1 January 2000 to 31 December 2009. Kaplan-Meier and Cox proportional hazard models were used to analyse the significance of clinical parameters, including age, sex, smoking history, body mass index (BMI), severity of airflow limitation, airway obstruction reversibility and overlap syndrome with hospitalisation due to respiratory problems or death.
  
  
  RESULTS
  Overlap syndrome patients were older, included smaller proportions of males and of smokers and had lower forced expiratory volume in 1 s (FEV1) (% predicted). Shorter hospitalisation-free and survival periods were noted among overlap syndrome patients. Overlap syndrome was significantly associated with risk of hospitalisation due to respiratory problems after adjusting for age, smoking history, BMI, FEV1 (% predicted) and changes in FEV1 (P < 0.001).
  
  
  CONCLUSIONS
  Asthma and COPD overlap syndrome is associated with a higher risk of hospitalisation due to respiratory problems than COPD alone.
authors.affiliation: Department of Allergy and Clinical Immunology, CHA Bundang Medical Center, CHA University, Seongnam, Republic of Korea.
authors.forename: M-A
authors.initials: MA
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Seoul Seonam Hospital, Ewha Womans University Medical Center, Seoul, Republic of Korea.
authors.forename: C S
authors.initials: CS
authors.lastname: Noh
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chungbuk National University Hospital, Chungbuk National University College of Medicine, Cheongju, Republic of Korea.
authors.forename: Y-J
authors.initials: YJ
authors.lastname: Chang
authors.affiliation: Department of Internal Medicine, Kangwon National University Hospital, Chuncheon, Republic of Korea.
authors.forename: Y-K
authors.initials: YK
authors.lastname: Hong
authors.affiliation: Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea.
authors.forename: J S
authors.initials: JS
authors.lastname: Lee
authors.affiliation: Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea.
authors.forename: S W
authors.initials: SW
authors.lastname: Lee
authors.affiliation: Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea.
authors.forename: S-D
authors.initials: SD
authors.lastname: Lee
authors.affiliation: Department of Pulmonary and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea.
authors.forename: Y-M
authors.initials: YM
authors.lastname: Oh
mesh_terms: D000368:Aged; D001249:Asthma / Q000453:epidemiology*; D002423:Cause of Death; D005260:Female; D005541:Forced Expiratory Volume; D006760:Hospitalization; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D016016:Proportional Hazards Models; D029424:Pulmonary Disease, Chronic Obstructive / Q000453:epidemiology*; D056910:Republic of Korea; D012189:Retrospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index; D062606:Tertiary Care Centers