Development of frailty index using ICD-10 codes to predict mortality and rehospitalization of older adults: An update of the multimorbidity frailty index

Objective: This study aims to develop an updated mFI (multimorbidity frailty index) using ICD-10-CM codes and to examine the association between frailty and all-cause mortality, unplanned hospitalization, and ICU admission by adopting the updated mFI in the contemporary ICD-10-CM era. Methods: From NHIRD, subjects aged 65–100 years with full National Health Insurance coverage in 2017 were included. We constructed the renewed mFI using ICD-10 CM codes (mFI-v10) by the cumulative deficit approach and categorized the study subjects according to the mFI-v10 quartiles: fit, mild frailty, moderate frailty, and severe frailty. Outcomes of interests (1-year mortality, unplanned hospitalization, and intensive care unit (ICU) admission) were assessed using Cox regression analyses, adjusted by sex and age. Results: Compared with the fit group, those with severe frailty were associated with a 4-fold (adjusted HR 3.86, 95% CI 3.54–4.20) higher risk for death at one year. Subjects with moderate frailty or mild frailty were associated with a 2.4-fold (adjusted HR 2.35, 95% CI 2.18–2.55) or 1.6-fold (adjusted HR 1.57, 95% CI 1.47–1.69) higher risk for death at one year than the fit group. Similar risk trends can also be observed in unplanned hospitalization and intensive care unit (ICU) admission among the study population. Conclusion: The renewed multimorbidity frailty index constructed from ICD-10 codes is associated with an increased risk of 1-year of all-cause mortality, unplanned hospitalization, and ICU admission. It can provide updated information contributing to risk stratification using frailty index in the ICD-10 era.