Frailty Index

About the Frailty Index

The FI (developed by Rockwood, Mitnitski et al) can be used in research and health settings as a measure of health status of older individuals as:

• Proxy measure of aging;
• Predictor of risk/vulnerability to poor outcomes.

The Frailty Index is defined as the proportion of deficits present in an individual out of the total number of age-related health variables considered.

FI Score = Number of health deficits present / Number of health deficits measured

For example, an elderly patient with 20 health deficits out of 50 considered has a FI of 0.4 whilst another elderly patient with 10 health deficits out of 50 considered, has a FI of 0.2.

A Frailty Index can be created by utilizing health deficits that are routinely collected in health assessments, such as chronic diseases, symptoms and signs, laboratory, imaging and echocardiographic abnormalities, example of cognitive impairments or disabilities in ADLs (activities of daily living).

There is a standard procedure for creating a frailty index (please study linked in the references below) that starts from solving the need to operationalize frailty (defined as increased vulnerability to adverse outcomes).

Across several frailty index measures and studies, people were found to accumulate deficits, on average, at about 0.03/year and the frailer the person was (the higher the deficit count) the more vulnerable they were found to adverse outcomes.

Estimates were found to be more stable and with sufficient accuracy for predicting adverse outcomes when at least 30-40 health deficits were considered.

The FI shows a consistent, sub-maximal limit at about 2/3 of the deficits that are considered. For example, if a frailty index is composed of 30 items, the most that anyone will have wrong with them is not 30, but 20.

Variables can be included in a frailty index if they satisfy the following 5 criteria:

1. Deficits must be associated with health status (for example, not be just age related);
2. A deficit's prevalence must generally increase with age (although there may be exceptions);
3. The chosen deficits must not saturate too early (for example presbyopia and age-related lens changes occur nearly universally by age 55 so saturate too early);
4. Chosen deficits must cover a range of systems (for example, not just cognitive impairment items);
5. Deficits must be the same from one iteration to the other of the index, if used serially on the same people.

References

Searle SD, Mitnitski A, Gahbauer EA, Gill TM, Rockwood K. A standard procedure for creating a frailty index. (2008) BMC Geriatrics. 8 (1): 24.

Peña FG, Theou O, Wallace L, Brothers TD, Gill TM, Gahbauer EA, Kirkland S, Mitnitski A, Rockwood K. Comparison of alternate scoring of variables on the performance of the frailty index. BMC Geriatr. 2014; 14: 25.