The Frailty Index
The frailty index (FI), developed by our group, is one of the leading paradigms for understanding frailty at population, personal, organ, and tissue levels (with cellular deficit evaluation in development). The frailty index is used in routine care all over the world, including in an electronic form in the National Health Service in England. To quantify the level of frailty of an individual, the frailty index approach focuses first on the number of their health deficits, and then on the nature of those deficits.
One of the strengths of this approach is that a frailty index can be constructed using existing clinical and population-based data: not every frailty index needs to include the same items to achieve closely comparable estimates in prevalence and rate of change. The frailty index is replicable across different databases because, as a state variable, it takes advantage of the high redundancy of the human organism.
Other advantages of this approach are:
- it can be applied to almost any health dataset
- it is a comprehensive assessment of health
- it provides a continuous score from fitness to frailty
- it is more sensitive to health changes when compared to other tools
- it does not have a ceiling or floor effect
The main challenge is that it needs at least 30 health variables to be included; if data are not already collected, 30 or more variables can be onerous to collect.
Frailty indices have been constructed in various population-based studies worldwide such as the American National Health and Nutrition Examination Survey, the Survey of Health and Ageing and Retirement in Europe, the Australian Longitudinal Study of Aging, the Beijing Longitudinal Study of Aging, the Mexican Health and Aging Study, and the Study on Global Ageing and Adult Health (China, Ghana, India, Mexico, Russia and South Africa). Frailty in Canada has been extensively investigated using data from the Canadian Study of Health and Aging (CSHA) and the National Population Health Survey (NPHS).
Our group has published over 100 papers on frailty using the CHSA and NPHS data. These studies were vital in setting the foundation for understanding the nature and quantification of frailty.
Specifically, they have shown that:
- the frailty index strongly predicts adverse outcomes including mortality, disability, and cognitive decline and it outperforms chronological age as a predictor of these outcomes;
- the distribution of frailty indices in community-living samples are left skewed (the majority of people are healthy with low frailty index scores);
- individuals do not exceed a limit of 0.7 in the frailty index (this appears to reflect the degree to which health problems can be tolerated);
- individual frailty index do not just increase with age, they can also decrease, reflecting improved health; and
- males have lower mean frailty index values than females of the same age, whereas females show better mean survival than males with the same frailty index value.
Searle SD, Mitnitski A, Gahbauer EA, Gill TM, Rockwood K. A standard procedure for creating a frailty index. BMC Geriatr. 2008 Sep 30;8:24.