Accuracy of diagnostic codes for identifying patients with ulcerative colitis and Crohn's disease in the Veterans Affairs Health Care System.

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.