title: The impact of paradoxical comorbidities on risk-adjusted mortality of Medicare beneficiaries with cardiovascular disease.
abstract: BACKGROUND
  Persistent uncertainty remains regarding assessments of patient comorbidity based on  administrative data for mortality risk adjustment. Some models include comorbid conditions that are associated with  improved mortality while other models exclude these so-called paradoxical conditions. The impact of these conditions on  patient risk assessments is unknown.
  
  
  OBJECTIVE
  To examine trends in the prevalence of conditions with a paradoxical  (protective) relationship with mortality, and the impact of including these conditions on assessments of risk adjusted  mortality.
  
  
  METHODS
  Patients age 65 and older admitted for acute myocardial infarction (AMI) or coronary artery bypass  graft (CABG) surgery during 1994 through 2005 were identified in Medicare Part A files. Comorbid conditions defined using  a common algorithm were categorized as having a paradoxical or non-paradoxical relationship with 30-day mortality, based  upon regression coefficients in multivariable logistic regression models.
  
  
  RESULTS
  For AMI, the proportion of patients  with one or more paradoxical condition and one or more non-paradoxical condition increased by 24% and 3% respectively  between 1994 and 2005. The odds of death for patients with one-or-more paradoxical comorbidities, relative to patients  with no paradoxical comorbidity, declined from 0.69 to 0.54 over the study period. In contrast, the risk associated  with having one or more non-paradoxical comorbidities increased from 2.66 to 4.62 for AMI. This pattern was even stronger  for CABG. Risk adjustment models that included paradoxical comorbidities found larger improvements, in risk-adjusted  mortality for AMI and CABG, over time than models that did not include paradoxical comorbidities.
  
  
  CONCLUSIONS
  The  relationship between individual comorbid conditions and mortality is changing over time, with potential impact on  estimates of hospital performance and trends in mortality. Development of a standard approach for handling conditions  with a paradoxical relationship to mortality is needed.
authors.affiliation: Iowa City Veterans Administration Medical Center, Center for Comprehensive Access and Delivery Research and Evaluation (CADRE), Iowa City, IA 52246, USA. Mary-vaughan-sarrazin@uiowa.edu
authors.forename: Mary S
authors.initials: MS
authors.lastname: Vaughan-Sarrazin
authors.forename: Xin
authors.initials: X
authors.lastname: Lu
authors.forename: Peter
authors.initials: P
authors.lastname: Cram
mesh_terms: D000368:Aged; D000465:Algorithms; D002318:Cardiovascular Diseases / Q000453:epidemiology / Q000401:mortality*; D015897:Comorbidity; D001026:Coronary Artery Bypass / Q000401:mortality / Q000706:statistics & numerical data; D005260:Female; D006761:Hospitals / Q000592:standards / Q000706:statistics & numerical data; D006801:Humans; D016015:Logistic Models; D008297:Male; D006278:Medicare / Q000706:statistics & numerical data*; D016344:Medicare Part A / Q000706:statistics & numerical data; D009203:Myocardial Infarction / Q000453:epidemiology / Q000401:mortality; D019984:Quality Indicators, Health Care / Q000706:statistics & numerical data; D011787:Quality of Health Care / Q000592:standards / Q000706:statistics & numerical data; D020379:Risk Adjustment / Q000706:statistics & numerical data*; D014481:United States / Q000453:epidemiology