Table 3.

Summary of frailty instruments used in the included studies

Instrument	Description	Characteristics of tool	Definition of frailty	Validationa	Comments
Clinical frailty scale (CFS) [3]	Nine-point scale based on subjective assessment of functional status	Scale ranges from very fit (CFS = 1) to very severely frail (CFS = 8) and terminally ill (CFS = 9). Examples: very fit people are robust, active, energetic, and motivated while very severely frail is defined as someone who is completely dependent, approaching end of life	Usually CFS ≥ 4	Yes	Scale is simple and easy to use. It can be used by a variety of healthcare professionals
Frailty index (FI) [37]	Deficit model of frailty assessment where the degree of frailty is calculated by dividing the total deficits by the total number items assessed	Usually 30–70 items are assessed. Any item can be included in the index as long as it meets the following criteria: Item deficits increase with age Item is associated with health Item does not saturate with increasing age Items must cover a range of systems	Usually FI > 0.2	Yes	Often based on a comprehensive geriatric assessment including cognition, functional status, and co-morbid illnesses. Large number of items included can be challenging for its routine use, although it can be imbedded in clinical systems to make use of existing data
Frailty phenotype (FP) [9]	Frailty tool based on the presence of physical phenotypic features	Calculated by the number of phenotypic features present: Weakness Slowness Physical activity Weight loss Self-reported exhaustion	Usually FP > 2	Yes	Focused on objective and self-reported criteria for physical function. No assessment of cognition

^aScale validated to correlate with risk of adverse events, adverse outcomes from medical interventions, need for hospitalization, need for institutionalization and death in non-ICU populations