Whilst it is important to be aware of what frailty looks like, it is equally important to understand what it is made up of. In other words, what is it that causes the physical weakening and slowing down which is so characteristic of frailty?
Essentially, frailty is the result of the build-up of lots of little things which ‘go wrong’ or ‘get worn out’ over a lifetime.
This is known as the cumulative deficit model of frailty and is based on the idea that in frailty it is the number of things that have ‘gone wrong’ that is more important than the exact nature of the individual problems.
The cumulative deficit model of frailty tends to focus upon physical status and determinants of frailty. It is based upon the importance of the accumulated effect on an individual of multiple health deficits at the same time and related to underlying physiological abnormalities. A deficit can be any symptom, sign, disease, disability or laboratory abnormality that is associated with age and adverse outcomes. It can cover mental as well as physical health and also impairments such as poor hearing and vision.
This approach results in the expression of frailty as a ‘frailty index’, which is simply a fraction which expresses the number of deficits found in any one individual divided by the total number of deficits possible in the measurement tool concerned.
This is a useful way of thinking about frailty because it means that counting these ‘deficits’ can be used as a way of measuring frailty, and this gives rise to tools for identifying and assessing frailty. Ths includes the electronic Frailty Index (eFI) which uses coded primary care data to produce the eFI. Further details about its development and use can be found here.
A person’s frailty index is an absolute measure and can change over time. It is therefore potentially more sensitive to change in frailty over time than the phenotype model. The nature of the deficits contributing to the frailty index can also provide some insight into the underlying causes of frailty and therefore offer some potential to guide interventions.