Updating and validating the Figueroa Frailty Index: transitioning from ICD-9 to ICD-10

BACKGROUND: The Figueroa Frailty Index (Figueroa-FI) is a claims-based frailty index developed using administrative Medicare claims data using International Classification of Disease (ICD) 9th revision. Updating to ICD-10 codes is essential for contemporary measurement. METHODS: ICD-9 codes were mapped to ICD-10 using Centers for Medicaid and Medicare Services (CMS) General Equivalence Mappings. Using a national cohort of Veterans aged ≥65 years, 2012-2019, annual prevalence trends for the 12 Figueroa-FI deficits were examined. Validity of Figueroa-FI was ascertained by examining adjusted annual HR of death and long-term institutionalization (LTI) for Veterans with 1 and ≥2 deficits vs 0, using Cox proportional hazards models. RESULTS: Annual cohorts of Veterans included 2.4 to 3.1 million Veterans, mean age 75 years, 97%-98% were male, 78%-80% White. Figueroa FI-ICD-10 includes 267 ICD-10 codes (vs 42 ICD-9 codes). Nine of the 12 Figueroa-FI deficits showed similar prevalence across the ICD-10 transition in 2016, while 3 displayed discontinuity. Veterans identified as frail were at increased risk of mortality and LTI. HR for death for FI of 1 vs 0 ranged from 1.97 to 2.02 over follow-up years, and HR of LTI from 2.75 to 2.92, while frail Veterans (FI ≥2) had hazards of death of 2.79 to 2.97 and hazards of LTI from 5.65 to 6.54. CONCLUSIONS: The updated Figueroa FI-ICD-10 maintains content validity, stability, and predictive validity for mortality and LTI in a contemporary cohort of Veterans aged ≥65 years, enabling frailty measurement using ICD-10 claims for clinical and research use.