Rationale: Population and health services research can be performed by linkage analysis of administrative data. However, the robustness of study results is determined by the accuracy of the diagnostic coding.
Objectives: To estimate the awareness, use and accuracy of the International Classification of Diseases, Ninth Revision (ICD-9) coding by physicians providing services for patients with Crohn's disease (CD) and ulcerative colitis (UC).
Methods: All Ontario gastroenterologists and a 10% random sample of internists, pediatricians, pediatric or general surgeons, and family physicians were surveyed by postal questionnaire to estimate the frequency and 95% CI of using codes 555 or 556 when billing for CD- and UC-related services, respectively. c2 tests were used for between-group comparisons.
Results: Of the physicians who were surveyed, 67.7% (416 of 614) responded; 258 of 391 (66%) who were still practising in Ontario saw patients with inflammatory bowel disease (IBD), and 54% had more than 10 IBD patients; 86.5% (95% CI 82.4% to 90.6%) were familiar with ICD-9 codes, and 91.4% (95% CI 88.1% to 95.6%) used the codes 555 (CD) or 556 (UC) for billing. Rates of ICD-9 use did not differ by sex but were used more frequently by those graduating after 1981 (P<0.02). Gastroenterologists used ICD-9 IBD codes 555 or 556 significantly more often than all other physicians (P=0.001). Most (more than 75%) Ontario physicians used ICD-9 IBD codes always or frequently when billing for IBD-related services. Few (10%) used these codes to bill for non-IBD-related problems.
Conclusions: These data suggest that there is acceptable use and accuracy of ICD-9 diagnostic coding for CD and UC services - comparable with results from studies of other diseases. Administrative data may thus be used to undertake epidemiological studies in IBD in Ontario.