Objectives: This study aims to address the knowledge gap and summarise the measurement for intrinsic capacity for the five WHO domains across different populations. It specifically aims to identify measurement tools, methods used for computation of a composite intrinsic capacity index and factors associated with intrinsic capacity among older adults.
Methods: We performed literature review in Medline, including search terms "aged" or "elderly" and "intrinsic capacity" for articles published from 2000 - 2020 in English. Studies which assessed intrinsic capacity in the five WHO domains were included. Information pertaining to study setting, methods used for measuring the domains of intrinsic capacity, computation methods for composite intrinsic capacity index, and details on tool validation were extracted.
Results: Seven articles fulfilling the inclusion criteria were included in the review. Of these, the majority were conducted in community settings (n=5) and were retrospective studies (n=6). The most commonly used tools for assessing intrinsic capacity were gait speed test and chair stand test (locomotion); handgrip-strength and mini-nutritional assessment (vitality); Mini-Mental State Examination (cognition); Geriatric Depression Scale (GDS) and Center for Epidemiological Studies Depression Scale (CES-D) (psychological), and self-reported vision and health questionnaires (sensory). Among the tools used to operationalise the domains, we found variations and non-concordance, especially in the vitality and psychological domains, which make inter-study comparison difficult. Validated scales were less commonly used for vitality and sensory domains. Biomarkers were used for locomotion, vitality, and sensory domains. Self-reported measures were mostly used in the psychological and sensory domains. Three studies operationalised a global score for intrinsic capacity, whereby scores from the individual domains were used to create a composite intrinsic capacity index, using two approaches: a) Structural equation modelling, and b) Sub-scores for each domain which were combined either by arithmetic sum or average.
Conclusion: We identified considerable variations in measurement instruments and processes which are used to assess intrinsic capacity, especially among the vitality and psychological domains. A standardized intrinsic capacity composite score for clinical or community settings has not been operationalised yet. Further validation via prospective studies of the intrinsic capacity concept and computation of composite score using validated scales are needed.
Keywords: Healthy aging; elderly; successful aging.