title: Accuracy of diagnostic codes for identifying patients with ulcerative colitis and Crohn's disease in the Veterans Affairs Health Care System.
abstract: BACKGROUND
  International Classification of Diseases-9 (ICD-9) codes are useful in clinical research; however, the validity of ICD-9 codes for inflammatory bowel disease (IBD) patients in multiple centers in the Veterans Affairs Health Care Systems (VA) has not been established. Our aim was to determine the accuracy of ICD-9 codes for Crohn's disease (CD) and ulcerative colitis (UC) in the VA.
  
  
  METHODS
  Patients with a diagnosis of IBD during 1999-2009 were identified by at least one ICD-9 code for CD (555.x) or UC (556.x) at the Houston and Ann Arbor VA Medical Centers and confirmed by chart review. A diagnosis of CD, UC, and IBD, unspecified (IBDU) was determined based on structured review of data in the VA medical records. Positive predictive values (PPV) were calculated for the codes using previously published ICD-9 algorithms.
  
  
  RESULTS
  A total of 1,871 patients were identified with ICD-9 codes for IBD. Of these patients, 1,298 (69 %) were confirmed to have IBD, with 541 CD (41 %), 707 UC (55 %), and 50 IBDU (4 %) patients. An algorithm of 2 or more codes with at least one from an outpatient encounter improved the PPV (0.83 and 0.89 for CD and UC, respectively) compared a single code algorithm (PPV 0.59 and 0.66, respectively).
  
  
  CONCLUSIONS
  Single ICD-9 codes are inadequate to accurately define IBD patients; however, ICD-9 code algorithms can be used to identify patients with UC or CD with high positive predictive value. The 2 code, at least 1 outpatient code algorithm was observed to have a high PPV and low miss rate.
authors.affiliation: Houston VA HSR&D Center of Excellence, Michael E. DeBakey Veteran Affairs Hospital, Houston, TX, USA, jkhou@bcm.edu.
authors.forename: Jason K
authors.initials: JK
authors.lastname: Hou
authors.forename: Mimi
authors.initials: M
authors.lastname: Tan
authors.forename: Ryan W
authors.initials: RW
authors.lastname: Stidham
authors.forename: John
authors.initials: J
authors.lastname: Colozzi
authors.forename: Devon
authors.initials: D
authors.lastname: Adams
authors.forename: Hashem
authors.initials: H
authors.lastname: El-Serag
authors.forename: Akbar K
authors.initials: AK
authors.lastname: Waljee
mesh_terms: D000465:Algorithms; D015331:Cohort Studies; D003093:Colitis, Ulcerative / Q000145:classification / Q000175:diagnosis*; D003424:Crohn Disease / Q000145:classification / Q000175:diagnosis*; D005260:Female; D006801:Humans; D038801:International Classification of Diseases / Q000592:standards*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014481:United States; D014493:United States Department of Veterans Affairs