Diagnostic Category Prevalence in 3 Classification Systems Across the Transition to the International Classification of Diseases, Tenth Revision, Clinical Modification

Key Points Question Was the transition from International Classification of Diseases, Ninth Revision, Clinical Modification ( ICD-9-CM ) to the Tenth Revision ( ICD-10-CM ) in October 2015 associated with changes in diagnostic category prevalence when diagnoses are grouped by classification system? Findings This interrupted time series analysis and cross-sectional study examined insurance claims for more than 18 million privately insured adults and children in the US from 2010 to 2017 and found instantaneous increases or decreases of 20% or more associated with the ICD-10-CM transition for nearly 1 in 6 (16%) diagnostic categories in 2 of 3 influential diagnostic classification systems. Meaning These findings suggest that diagnostic classification systems developed with ICD-9-CM data may need to be refined for use with ICD-10-CM data for disease surveillance, performance assessment, or risk-adjusted payment.