Objective To assess the utility and cost of using routinely collected inpatient data for large-scale audit.

Design Comparison of audit data items collected nationally in a designed audit of inflammatory bowel disease (UK IBD audit) with routinely collected inpatient data; surveys of audit sites to compare costs.

Setting National Health Service hospitals across England, Wales and Northern Ireland that participated in the UK IBD audit.

Patients Patients in the UK IBD audit.

Interventions None.

Main outcome measures Percentage agreement between designed audit data items collected for the UK IBD audit and routine inpatient data items; costs of conducting the designed UK IBD audit and the routine data audit.

Results There were very high matching rates between the designed audit data and routine data for a small subset of basic important information collected in the UK IBD audit, including mortality; major surgery; dates of admission, surgery, discharge and death; principal diagnoses; and sociodemographic patient characteristics. There were lower matching rates for other items, including source of admission, primary reason for admission, most comorbidities, colonoscopy and sigmoidoscopy. Routine data did not cover most detailed information collected in the UK IBD audit. Using routine data was much less costly than collecting designed audit data.

Conclusion Although valuable for large population-based studies, and less costly than designed data, routine inpatient data are not suitable for the evaluation of individual patient care within a designed audit.