Shifts in Alcohol-Related Diagnoses After the Introduction of International Classification of Diseases, Tenth Revision, Clinical Modification Coding in U.S. Hospitals: Implications for Epidemiologic Research

Background: In October 2015, the United States transitioned healthcare diagnosis codes from the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM), to the Tenth Revision (ICD-10-CM). Trend analyses of alcohol-related stays could show discontinuities solely from the change in classification systems. This study examined the impact of the ICD-10-CM coding system on estimates of hospital stays involving alcohol-related diagnoses.

Methods: This analysis used 2014 to 2017 administrative data from the Agency for Healthcare Research and Quality Healthcare Cost and Utilization Project State Inpatient Databases for 17 states. Quarterly ICD-9-CM data from second quarter 2014 through third quarter 2015 were concatenated with ICD-10-CM data from fourth quarter 2015 through first quarter 2017. Quarterly counts of alcohol-related stays were examined overall and then by 6 diagnostic subgroups: withdrawal, abuse, dependence, alcohol-induced mental disorders (AIMD), nonpsychiatric alcohol-induced disease, and intoxication or toxic effects. Within each group, we calculated the difference in the average number of stays between ICD-9-CM and ICD-10-CM coding periods.

Results: On average, the number of stays involving any alcohol-related diagnosis in the 6 quarters before and after the ICD-10-CM transition was stable. However, substantial shifts in stays occurred for alcohol abuse, AIMD, and intoxication or toxic effects. For example, the average quarterly number of stays involving AIMD was 170.7% higher in the ICD-10-CM period than in the ICD-9-CM period. This increase was driven in large part by 1 ICD-10-CM code, Alcohol use, unspecified with unspecified alcohol-induced disorder.

Conclusions: Researchers conducting trend analyses of inpatient stays involving alcohol-related diagnoses should consider how ongoing modifications in the ICD-10-CM code system and coding guidelines might affect their work. An advisable approach for trend analyses across the ICD-10-CM transition is to aggregate diagnosis codes into broader, clinically meaningful groups-including a single global group that encompasses all alcohol-related stays-and then to select diagnostic groupings that minimize discontinuities between the 2 coding systems while providing useful information on this important indicator of population health.