Background The aim of the study was to review systematically the literature measuring the accuracy of routine UK hospital statistics that classify patients on discharge.
Methods A systematic review was carried out of studies comparing routine discharge statistics about an episode of hospital care with the original medical record. Dual quality assessment and extraction was completed for included studies. Qualitative and descriptive analyses were undertaken. Additional comparisons of factors that could potentially introduce systematic variation in coding accuracy were also undertaken.
Results Thirty studies were identified, of which 21 were included in the review. Twelve of these were conducted in England and Wales, and nine in Scotland. The majority assessed the accuracy of a single diagnosis, or selection of diagnoses in a limited range of hospital settings. The median coding accuracy rates were 91 per cent for diagnostic codes and 69.5 per cent for operation or procedure codes in studies in England or Wales; 82 per cent for diagnostic codes and 98 per cent for operation or procedure codes in Scottish studies. There were no significant differences in coding accuracy over time or in the type or rarity of the codes being assessed. Accuracy rates were higher for ICD7 codes (median 96.5 per cent) than for ICD8 (median 87 per cent) or ICD9 (median 77 per cent).
Conclusions Coding accuracy on average is high in the United Kingdom, especially for operations and procedures. However, policy-makers, planners and researchers need to recognize and account for the degree of inaccuracy in routine hospital information statistics. Further research is needed into methods of improving and maintaining coding accuracy.