In 2015, the implementation of the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) was viewed as a significant policy change with the potential to affect how researchers gather and interpret data on injury morbidity trends. There was speculation that by changing the diagnostic codes applied to injuries treated by clinicians, the transition from ICD-9-CM to ICD-10-CM could have a significant effect on the reporting of injury data used to inform policy as well as clinical practices.
To assess the impact of the move to the ICD-10-CM on injury research, investigators with the Kentucky Injury Prevention and Research Center at the University of Kentucky College of Public Health completed a study, the results of which now appear in Injury Epidemiology, wherein they used data from Kentucky hospitals to demonstrate the use of a statistical method to estimate the effect of the coding transition on injury hospitalization trends, as well as interpretation of significant changes in injury trends in the context of differences between ICD-9-CM and ICD-10-CM, the new ICD-10-CM-specific coding guidelines, and proposed ICD-10-CM-based-framework for reporting of injuries by intent and mechanism.
With colleagues from the Medical College of Wisconsin and the Colorado Department of Public Health and the Environment, the Kentucky investigators used segmented regression analysis for statistical modeling of interrupted time series monthly data to evaluate the effect of the transition to ICD-10-CM on Kentucky hospitalizations’ external-cause-of-injury completeness (the percentage of records with principal injury diagnoses supplemented with external-cause-of-injury codes), as well as injury hospitalization trends by intent or mechanism. They examined data from January 2012 to December 2017.
The investigators found that the segmented regression analysis showed an immediate significant drop in external-cause-of-injury completeness during the transition month, but returned to its pre-transition levels in November 2015. There was a significant immediate change in the percentage of injury hospitalizations coded for unintentional (3.34 percent) and undetermined intent (- 3.39 percent). There were also immediate significant changes in the recorded levels of injury hospitalization rates due to “poisoning”, “suffocation”, “struck by/against”, “other transportation”, “unspecified mechanism” and other not-specified-elsewhere mechanisms. Significant change in slope after the transition (without immediate level change) was identified for “assault”, “firearm”, “cut/pierce”, and “motor vehicle traffic injury” rates. The observed trend changes reflected structural and conceptual features of ICD-10-CM coding (e.g., poisoning and suffocations are now captured via diagnosis codes only), new coding guidelines (e.g., requiring coding of injury intent as “accidental” if it is unknown or unspecified), and CDC-proposed external-cause-of-injury code groupings by injury intent and mechanism. Researchers can replicate this methodology assessing trends in injuries or other ICD-10-CM-coded conditions using administrative billing data sets.
The investigators conclude that the CDC ‘s Proposed Framework for Presenting Injury Data Using ICD-10-CM External Cause of Injury Codes provided a logical transition from the ICD-9-CM-based matrix on injury hospitalization trends by intent and mechanism. They note that “our findings are intended to raise awareness that changes in the ICD-10-CM coding system must be understood to assure accurate interpretation of injury trends.”