title: ICD-9 tobacco use codes are effective identifiers of smoking status.
abstract: OBJECTIVE
  To evaluate the validity of, characterize the usage of, and propose potential research applications for International Classification of Diseases, Ninth Revision (ICD-9) tobacco codes in clinical populations.
  
  
  METHODS
  Using data on cancer cases and cancer-free controls from Vanderbilt's biorepository, BioVU, we evaluated the utility of ICD-9 tobacco use codes to identify ever-smokers in general and high smoking prevalence (lung cancer) clinic populations. We assessed potential biases in documentation, and performed temporal analysis relating transitions between smoking codes to smoking cessation attempts. We also examined the suitability of these codes for use in genetic association analyses.
  
  
  RESULTS
  ICD-9 tobacco use codes can identify smokers in a general clinic population (specificity of 1, sensitivity of 0.32), and there is little evidence of documentation bias. Frequency of code transitions between 'current' and 'former' tobacco use was significantly correlated with initial success at smoking cessation (p<0.0001). Finally, code-based smoking status assignment is a comparable covariate to text-based smoking status for genetic association studies.
  
  
  CONCLUSIONS
  Our results support the use of ICD-9 tobacco use codes for identifying smokers in a clinical population. Furthermore, with some limitations, these codes are suitable for adjustment of smoking status in genetic studies utilizing electronic health records.
  
  
  CONCLUSIONS
  Researchers should not be deterred by the unavailability of full-text records to determine smoking status if they have ICD-9 code histories.
authors: Center for Human Genetics Research, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
authors: Laura K
authors: LK
authors: Wiley
authors: Anushi
authors: A
authors: Shah
authors: Hua
authors: H
authors: Xu
authors: William S
authors: WS
authors: Bush
mesh_terms: D059019:Clinical Coding; D006801:Humans; D038801:International Classification of Diseases; D012680:Sensitivity and Specificity; D012907:Smoking
keywords: Electronic Health Records; International Classification of Diseases; Phenotype
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