Disability and co-morbidity in relation to frailty: How much do they overlap?
Introduction
Although many older adults report being healthy, 91% have one or more chronic conditions, 40% live with a disability and about 23% are frail (Public Health Agency of Canada, 2006, Rockwood et al., 2011). Frailty is non-controversially understood as increased vulnerability to adverse health outcomes of people of the same chronological age (Rockwood et al., 1994, Theou and Kloseck, 2007, Abellan van Kan et al., 2010, Clegg and Young, 2011). The consideration of older adults’ frailty status is fundamental to their care (Theou and Rockwood, in press). For example, a severely frail 70-year-old person may not survive an aggressive medical treatment such as a major surgery, even though they are comparatively young, and may benefit more from innovative processes of care. Likewise, a fit 84-year-old might well withstand such a procedure despite being older.
Frailty's operationalization varies chiefly between groups who follow what is known as the “phenotypic” approach (Fried et al., 2001, Bergman et al., 2004) versus those who follow a deficit accumulation approach to defining frailty (Mitnitski et al., 2001, Kulminski et al., 2006). The frailty phenotype of five items (Fried et al., 2001) – sometimes fewer (Ensrud et al., 2009) – holds that while frailty is related to disability and co-morbidity, it is conceptually distinct (Fried et al., 2004). For this reason, some commentators recommend against including disability and co-morbidity markers as part of any frailty definition (Fried et al., 2004, Abellan van Kan et al., 2008). The deficit accumulation approach views frailty as a stochastic process in a redundant system of multiply dependent items which on average is accumulating deficits that impair physiological reserve (Rockwood et al., 2010). For this reason, in terms of understanding system behavior, knowing exactly what is wrong is less important than knowing how many things have gone wrong (Mitnitski et al., 2005). The deficit accumulation approach to frailty recommends against excluding items a priori, as long as each individual items included in a FI meets the criteria to be a deficit: item should increase with age but not become saturated (i.e. not be represent in everyone by some comparatively young age), be associated with an adverse outcome, have <5% missing data and occur at some detectable threshold (e.g. a prevalence of least 5%) (Mitnitski et al., 2001, Searle et al., 2008). Although some studies note differences in the predictive power of the two approaches (Kulminski et al., 2008, Hubbard et al., 2009a), frailty can have a tremendous impact on older individuals, their families, and society regardless of how it is defined (Clegg and Young, 2011). Even so, words matter, so knowing whether a frailty definition includes, excludes or is indifferent to disability and co-morbidity is important in interpreting studies about frailty and its consequences.
Although conceptually distinct, frailty disability and co-morbidity clearly are related (Fried et al., 2004, Levers et al., 2006, Inouye et al., 2007). Frail older adults are often described interchangeably as disabled with multiple chronic diseases (Markle-Reid and Browne, 2003, Topinkova, 2008) because of these concepts’ conceptual similarity, co-occurrence and relationship with adverse outcomes (Al Snih et al., 2009). Given theoretical distinctiveness in the face of empirical overlap, examining how frailty, disability, and co-morbidities occur and how they relate to adverse outcomes is vital, given the clinical and public health importance of these concepts. For these reasons, we undertook a study aiming to: (1) estimate the proportion of frail participants experiencing disability and/or co-morbidities; (2) determine the level of the FI that ADL function becomes impaired and chronic diseases accumulate, and; (3) examine whether disability and co-morbidities should be included in the FI in order to predict mortality risk.
Section snippets
Study design and participants
This is a secondary analysis of the clinical data from the second wave of the CSHA, a prospective population-based cohort study that began in 1991 (CSHA Working Group, 1994). Briefly, at baseline 9008 community-dwelling adults aged 65 years and over were randomly sampled from 36 study centers in all 10 Canadian provinces. They were screened for cognitive impairment using a questionnaire that included the modified Mini-Mental State Examination (3MS) (Teng and Chui, 1987). People who screened
Results
Women were older, more frail and experienced more ADL impairments whereas men reported more chronic conditions and had a higher death rate (Table 1). The proportion of older adults reporting disability and co-morbidity was similar when either of the FI or the frailty phenotype measures was used. Regardless of how frailty was measured, fewer than 10% of people who were frail did not experience any disability or co-morbidity (Fig. 1). Similar overlap was found when we examined separately the
Discussion
We examined the association of frailty with disability and co-morbidity in a population-based clinical study. Regardless of whether disability and co-morbidity were included in a FI based on the accumulation of deficits, the risk of death increased as the level of frailty increased. Even so, when they were excluded from the FI both disability and co-morbidity contributed to the prediction of mortality. ADL limitations and chronic diseases occurred more often among people with the highest levels
Conflict of interest statement
KR research is supported by operating grants from the Canadian Institutes of Health Research (MOP-209888) and the Nova Scotia Health Research Foundation (MED2006-2086). KR receives funding from the Dalhousie Medical Research Foundation as Kathryn Allen Weldon Professor of Alzheimer Research. KR reports applying for funding to commercialize a version of the FI based on a comprehensive geriatric assessment.
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