Frailty Index

Definition

A frailty index is a quantitative measure of frailty based on the accumulation of health deficits. It is usually calculated as the proportion of measured deficits an individual has, such as symptoms, diseases, disabilities, abnormal test results, or functional limitations, out of the total number of deficits assessed. [1] [2] [3]

Why It Matters in Ageing Research

The frailty index matters because it provides a way to summarise biological vulnerability and loss of reserve across multiple body systems. In ageing research and clinical studies, higher frailty index scores are associated with increased risk of adverse outcomes, including disability, hospitalisation, institutionalisation, and mortality. It is often used to distinguish chronological age from measurable health status in older adults. [4] [5] [6]

Common Confusion

• A frailty index is not the same as chronological age; people of the same age can have very different frailty scores.
• The frailty index is one approach to measuring frailty; another common approach is the frailty phenotype.
• A higher frailty index usually indicates greater vulnerability, but interpretation depends on which deficits were measured and the population studied.

Related Reading

• Frailty
• Biological Age
• Healthspan
• Intrinsic Capacity

References

1. Mitnitski, A. B., Mogilner, A. J., & Rockwood, K. (2001). Accumulation of deficits as a proxy measure of aging. https://doi.org/10.1101/gr.133801
2. Rockwood, K., & Mitnitski, A. (2007). Frailty in relation to the accumulation of deficits. https://doi.org/10.1093/gerona/62.7.722
3. Searle, S. D., Mitnitski, A., Gahbauer, E. A., Gill, T. M., & Rockwood, K. (2008). A standard procedure for creating a frailty index. https://doi.org/10.1186/1471-2318-8-24
4. Clegg, A., Young, J., Iliffe, S., Rikkert, M. O., & Rockwood, K. (2013). Frailty in elderly people. https://doi.org/10.1016/S0140-6736(12)62167-9
5. Fried, L. P., Tangen, C. M., Walston, J., et al. (2001). Frailty in older adults: evidence for a phenotype. https://doi.org/10.1093/gerona/56.3.M146
6. Rockwood, K., Song, X., MacKnight, C., Bergman, H., Hogan, D. B., McDowell, I., & Mitnitski, A. (2005). A global clinical measure of fitness and frailty in elderly people. https://doi.org/10.1503/cmaj.050051