Identifying Older Adults With Serious Illness: Transitioning From ICD-9 to ICD-10.

Context: Identifying the seriously ill population is integral to improving the value of health care. Efforts to identify this population using existing data are anchored to a list of severe medical conditions (SMCs) using diagnostic codes. Published approaches have used International Classification of Diseases, Ninth Revision (ICD-9) codes, which has since been replaced by ICD-10.

Objectives: We translated SMCs from ICD-9 to ICD-10 using a refined code list. We aimed to test the hypothesis that people identified by ICD-9 or ICD-10 codes would have similar Medicare costs, health care utilization, and mortality.

Methods: Using data from the National Health and Aging Trends Study linked to Medicare claims, we compared samples from periods using ICD-9 (2014) and ICD-10 (2016). We included participants with six-month fee-for-service Medicare data before their interview date who had an SMC identified within that period. We compared the groups' demographic, functional, and medical characteristics and followed up them for six months to compare outcomes.

Results: Among subjects in the 2016 (ICD-10) sample, 19.9% were hospitalized, 24.6% used the emergency department, 7.2% died, and average Medicare spending totaled $9902.04 over six months of follow-up. We observed no significant differences between the 2014 and 2016 samples (P > 0.05); both samples represent 18% of Medicare fee-for-service beneficiaries.

Conclusion: Identifying the seriously ill population using currently available data requires using ICD-10 to define SMCs. Routine measurement of function, quality of life, and caregiver strain will further enhance the identification process and efficiently target palliative care services and appropriate quality measures.