title: Adaptation and validation of the Charlson Index for Read/OXMIS coded databases.
abstract: BACKGROUND
  The Charlson comorbidity index is widely used in ICD-9 administrative data, however, there is no translation for Read/OXMIS coded data despite increasing use of the General Practice Research Database (GPRD). Our main objective was to translate the Charlson index for use with Read/OXMIS coded data such as the GPRD and test its association with mortality. We also aimed to provide a version of the comorbidity index for other researchers using similar datasets.
  
  
  METHODS
  Two clinicians translated the Charlson index into Read/OXMIS codes. We tested the association between comorbidity score and increased mortality in 146 441 patients from the GPRD using proportional hazards models.
  
  
  RESULTS
  This Read/OXMIS translation of the Charlson index contains 3156 codes. Our validation showed a strong positive association between Charlson score and age. Cox proportional models show a positive increasing association with mortality and Charlson score. The discrimination of the logistic regression model for mortality was good (AUC = 0.853).
  
  
  CONCLUSIONS
  We have translated a commonly used comorbidity index into Read/OXMIS for use in UK primary care databases. The translated index showed a good discrimination in our study population. This is the first study to develop a co-morbidity index for use with the Read/OXMIS coding system and the GPRD. A copy of the co-morbidity index is provided for other researchers using similar databases.
authors.affiliation: Department of Primary Health Care, University of Oxford, Old Road Campus, Oxford OX3 7LF, UK. nada.khan@dphpc.ox.ac.uk
authors.forename: Nada F
authors.initials: NF
authors.lastname: Khan
authors.forename: Rafael
authors.initials: R
authors.lastname: Perera
authors.forename: Stephen
authors.initials: S
authors.lastname: Harper
authors.forename: Peter W
authors.initials: PW
authors.lastname: Rose
mesh_terms: D015510:Clinical Medicine / Q000145:classification; D015897:Comorbidity; D016208:Databases, Factual; D005194:Family Practice; D049673:History, 20th Century; D006801:Humans; D016015:Logistic Models; D009026:Mortality; D011320:Primary Health Care / Q000145:classification; D016016:Proportional Hazards Models; D012984:Software; D018875:Vocabulary, Controlled / Q000266:history