Risk of Duplicate ICD Codes for Orthopedic and Injury Related Research.

The World Health Organization's International Classification of Diseases (ICD) has become the international standard diagnostic classification for reporting morbidity and mortality. In 2015, the United States transitioned from the 9th to 10th Revision. The update was necessary due to major structural limitations of the ICD-9 system. Concerns of the transition mainly centered around clinical usage and cost; however, there were concerns for overlapping codes with the same classification but different meanings between the two versions. Duplicate codes could pose an issue for big data retrospective studies that overlap between the two systems. Therefore, the goals of this study are to further explore and identify duplicate ICD codes between the systems. ICD-9-CM and ICD-10-CM code files were obtained from the Centers for Medicare & Medicaid Services. There were 14,567 ICD-9-CM codes and 91,737 unique ICD-10-CM codes tabulated. Duplicated items between the files were isolated. Four hundred sixty-nine duplicate codes were identified, consisting of 39 E Codes and 430 V Codes. These twin codes contain classifications for external causes of injury and factors influencing health status and contact with health services. Therefore, special attention should be drawn to retrospective research involving methods of injury spanning ICD-9 and ICD-10 systems.