Operationalization of Intrinsic Capacity in Older People and Its Association With Subsequent Disability, Hospital Admission and Mortality: Results From The English Longitudinal Study of Ageing

\Background: Intrinsic capacity (IC) is a new concept in the healthy aging field and has many operationalized definitions. In this study, we operationalized IC using item response theory in the English Longitudinal Study of Ageing (ELSA) and tested the predictive value of the scale using a subsequent functional ability, mortality, and hospital admission. Methods: IC was measured at baseline (2004, Wave 2) using 14 dichotomous indicators: word recall, orientation in time, balance, chair rises, walking speed, upper mobility, lower mobility, eyesight, hearing, grip strength, body mass index, waist circumference, depressive symptoms, and life satisfaction. A 2-parameter item response theory model was used to generate a scale of IC at baseline. Logistic regression was used for the prediction of subsequent difficulties, measured by difficulties with >= 1 activities of daily living (ADLs) and << 1 instrumental activities of daily living (IADLs) at 4 and 8 years after baseline. Competing risk and Cox regressions were employed to test the prediction of hospital admission and mortality, respectively, over a 14-year follow-up. Results: IC scores were generated for 4 545 individuals aged on average 70.8 years (standard deviation [SD] 7.93). Better baseline IC scores were associated with reduced risk of subsequent difficulties with ADLs and IADLs, hospital admission (subdistribution hazard ratios [SHR] = 0.99, 95% confidence interval [CI] 0.98-0.99), and mortality (hazard ratios [HR] = 0.98, 95% CI 0.98-0.99), when adjusted for sociodemographic and health-related covariates. Conclusion: These results suggest the utility of this IC score as a measure of risk for future adverse outcomes in older people, potentially above that indicated by other sociodemographic and health-related factors.