Validation and Comparison of Two Frailty Indexes: The MOBILIZE Boston Study

Frailty has become a particularly important geriatric topic since a 1990 American Medical Association report emphasized the growing population of vulnerable older adults. 1 This vulnerable population has been identified as older adults with an intrinsic vulnerability to stressors and increased risk for decline and adverse health-related characteristics such as disability and comorbidity, and has been described as frail. For reasons related to difficulties distinguishing these entities, and because many factors have been reported to be associated with frailty in older adults, there is no single consensus definition of frailty despite numerous definitions proposed by researchers. There is general agreement in the literature that frailty is a biologic syndrome of decreased reserve and resistance to stressors resulting from cumulative declines across multiple physiologic systems that cause vulnerability to adverse outcomes. 2 In an attempt to solidify the concept of frailty and operationalize its definition, Fried et al. 2 proposed a phenotype of frailty involving at least 3 of the following 5 components: unintentional weight loss, self-reported reduced energy level, reduced grip strength, slow walking speed, and a low level of physical energy. Using a frailty index based on this phenotype, Fried et al. and other researchers 2-8 have reported its association with falls, hospitalization, disability, and death. This index has been useful in identifying frail older adults, though its use is impractical in the clinical setting. Assessing strength, walking speed, and physical activity (3 components of this index) not only depends on gender and body mass but also requires knowledge of the underlying distribution of the measure in a given population. Moreover, assessing some of these components may not be feasible. For example, physical activity assessments and timed walks are often impractical to evaluate in a clinic due to schedule and space constraints. 6 Recently, Ensrud et al. 6 proposed a simpler frailty index, requiring at least 2 of 3 components (weight loss, the inability to rise from a chair 5 times without the use of arms, and self-reported reduced energy level). This index might be more suitable for assessing frailty in a busy clinical practice setting. Based on a prospective cohort study (N=6701) designed to examine osteoporosis and fractures in older women, Ensrud et al. 6 compared their frailty index to the Fried et al. frailty index on outcomes such as falls, recurrent falls, disability, fractures and death. Both indexes were strongly associated with these outcomes and their effect measures (i.e., hazard ratios and odds ratios) were very similar. Ensrud et al. concluded that their simpler index had very similar predictive properties compared to the Fried et al. frailty index, provided a useful definition of frailty, and could be used to identify older women at risk of adverse health outcomes in clinical practice setting. However, one important shortcoming of this study was its limited generalizability, as it did not include men or African-American women. The objective of this study was to validate and compare these two indexes using an independent diverse sample of men and women (including African-Americans). We examined the indexes' ability to predict recurrent falls, overnight hospitalizations, emergency room visits, and their association with disability, chronic medical conditions, self-reported health, physical function, cognitive function (including executive function) and depression. To our knowledge, this is the first validation and comparison of these two indexes using an independent data source that includes men and African-American women. It is also the first to examine executive function measures across frailty levels.