Extent and consequences of misclassified injury diagnoses in a national hospital discharge registry.
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.


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).


CONCLUSIONS
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.
Department of Surgical Sciences, Anesthesiology and Intensive Care, Uppsala University, Uppsala, Sweden.
Monica Frick
MF
Bergström
Liisa
L
Byberg
Håkan
H
Melhus
Karl
K
Michaelsson
Rolf
R
Gedeborg
D003951:Diagnostic Errors / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D015601:Injury Severity Score; D008297:Male; D017063:Outcome Assessment, Health Care; D010351:Patient Discharge; D012372:ROC Curve; D012042:Registries / Q000706:statistics & numerical data; D013548:Sweden / Q000453:epidemiology; D014947:Wounds and Injuries / Q000145:classification* / Q000175:diagnosis