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Extent and consequences of misclassified injury diagnoses in a national hospital discharge registry
  1. Monica Frick Bergström1,
  2. Liisa Byberg2,3,
  3. Håkan Melhus4,
  4. Karl Michaelsson2,3,
  5. Rolf Gedeborg1,2
  1. 1Department of Surgical Sciences, Anesthesiology and Intensive Care, Uppsala University, Uppsala, Sweden
  2. 2Uppsala Clinical Research Center, Uppsala University, Uppsala, Sweden
  3. 3Department of Surgical Sciences, Orthopedics, Uppsala University, Uppsala, Sweden
  4. 4Department of Medical Sciences, Uppsala University, Uppsala, Sweden
  1. Correspondence to Dr Rolf Gedeborg, Uppsala University, UCR/Scheele Dag Hammarskjölds väg 50A, 3tr Science Park, SE-751 85 Uppsala, Sweden; rolf.gedeborg{at}


Background Classification of injuries and estimation of injury severity on the basis of ICD-10 injury coding are powerful epidemiological tools. Little is known about the characteristics and consequences of primary coding errors and their consequences for such applications.

Materials and methods From the Swedish national hospital discharge register, 15 899 incident injury cases primarily admitted to the two hospitals in Uppsala County between 2000 and 2004 were identified. Of these, 967 randomly selected patient records were reviewed. Errors in injury diagnosis were corrected, and the consequences of these changes were analysed.

Results Out of 1370 injury codes, 10% were corrected, but 95% of the injury codes were correct to the third position. In 21% (95% CI 19% to 24%) of 967 hospital admissions, at least one ICD-10 code for injury was changed or added, but only 13% (127) had some change made to their injury mortality diagnosis matrix classification. Among the cases with coding errors, the mean ICD-based injury severity score changed slightly (difference 0.016; 95% CI 0.007 to 0.032). The area under the receiver operating characteristics curve was 0.892 for predicting hospital mortality and remained essentially unchanged after the correction of codes (95% CI for difference –0.022 to 0.013).

Conclusion Errors in ICD-10-coded injuries in hospital discharge data were common, but the consequences for injury categorisation were moderate and the consequences for injury severity estimates were in most cases minor. The error rate for detailed levels of cause-of-injury codes was high and may be detrimental for identifying specific targets for prevention.

  • Injury
  • registry
  • ICD-10
  • healthcare surveys
  • external cause of injury
  • database
  • e-code
  • methods

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  • Funding Uppsala University. The study sponsor had no role in the study design, in the collection, analysis and interpretation of data, in the writing of the report, or in the decision to submit the paper for publication.

  • Competing interests None.

  • Ethics approval This study was conducted with the approval of the Regional Human Ethics Committee, Uppsala, Sweden.

  • Provenance and peer review Not commissioned; externally peer reviewed.