Frailty index (deficit accumulation)

The deficit-accumulation frailty index, described by Mitnitski and Rockwood, measures frailty as the proportion of possible health deficits a person has. Deficits can be symptoms, diagnoses, disabilities or abnormal test results. The index is the number of deficits present divided by the number counted, so it runs from 0 to 1.

The approach works with any reasonable set of deficits, typically 30 or more, as long as they are health-related, accumulate with age and do not saturate too early. Across many populations the index rarely exceeds about 0.7, a practical upper limit beyond which survival is very short.

Originally developed for older adults, the index is increasingly used in surgical and congenital populations to describe how frail patients become over a lifetime.