Establishment of Clinical Construct of Intrinsic Capacity in Older Adults and Its Prediction of Functional Decline

The World Health Organization has conceptualised the health and healthcare of older adults around the concept of healthy ageing. Healthy ageing is defined as "the process of developing and maintaining the functional ability that enables well-being in older age". This functional ability is the sum of two key factors: intrinsic capacity and interacting environment. This concept of intrinsic capacity encompasses a wide spectrum of health characteristics including the physiological and psychological changes associated with the ageing process. In general, IC declines from a high and stable state to an impaired status as people age. Monitoring individuals for changes in intrinsic capacity in the context of their environment will provide a holistic method of tracking the functioning of older adults at both a population and individual level, providing an opportunity to address any reversible factors of decline. However, this would require a clear and objective conceptualisation of the concept of intrinsic capacity.

One hundred subjects were recruited via invitation by advertisement on the institute campus. Study participants underwent detailed physical examination and measurement of various physical and chemical biomarkers which were likely to represent intrinsic capacity as evidenced by the literature review. Outcomes measured were a decline in ADL, IADL, mortality and hospitalisation over a follow-up period of six months. Exploratory factor analysis (EFA) was done to obtain a clinical construct of the proposed entity of intrinsic capacity. Unpaired t-test and univariate logistic regression were used to check for the association between the composite score (IC) and its domains with the decline in ADL, IADL, mortality and hospitalisation.

One composite score (composite IC score) and eight subfactors emerged. The composite score and subfactor domains showed good construct validity. Composite intrinsic capacity score and subdomains of strength and cognition were significantly different among subjects with and without ADL and IADL decline. Univariate logistic regression showed that composite intrinsic capacity score was a predictor of decline in ADL and IADL even after adjusting for age, sex, comorbidity status and education level of the subject with an adjusted odds ratio of 0.99 and 0.98, respectively. Subdomains of strength and cognition also predicted a decline in ADL and IADL independently.

The development of an objective construct of the concept of intrinsic capacity, using commonly measured clinical and biochemical parameters, is feasible and predictive of the subsequent functionality of an individual.