Quality of ICD-10 colorectal cancer diagnosis codes in the Danish National Registry of Patients

This study examined the quality of International Classification of Diseases-10 colorectal cancer (CRC) diagnosis coding in the Danish National Registry of Patients (DNRP), using the Danish Cancer Registry (DCR) as a reference. We included all patients in Denmark with a CRC diagnosis in the DNRP and/or in the DCR from 2001 through 2006. Data quality was evaluated by estimating completeness and positive predictive value (PPV) of data in different subcategories of patients. We estimated mortality and date of diagnosis, to evaluate the effect of potential differences in data quality. Overall completeness of data in the DNRP for CRC was 93.4% [95% confidence interval (CI): 93.1-93.7] and the PPV was 88.9% (95% CI: 88.5-89.2). Completeness and PPV improved during the study period. However, the completeness of data for patients >75 years in the 2001-2003 period [88.8% (95% CI: 87.8-89.6)] was lower than average, and cancers in more unspecific locations and cancers in the colorectal junction also had lower estimates (below 90%). There were no differences in survival estimates in the DNRP compared to the DCR. In conclusion, this study shows high CRC data quality in the DNRP measured by completeness and PPV, except in a few subgroups.