The Clinical Frailty Scale score places the patient into one of nine descriptive categories. Scores 1-3 represent non-frail individuals: Very Fit (1) describes people who exercise regularly and are among the fittest for their age; Well (2) describes people without active disease but less fit than category 1; and Managing Well (3) describes people whose medical problems are well controlled but who are not regularly active. Score 4 (Vulnerable) describes people who are not dependent on others but whose symptoms limit activities — this is a transitional state between robust and frail.

Scores 5-8 represent progressive degrees of frailty: Mildly Frail (5) patients need help with instrumental activities of daily living (finances, transportation, housework); Moderately Frail (6) patients need help with both instrumental and some basic activities; Severely Frail (7) patients are completely dependent for personal care but medically stable; and Very Severely Frail (8) patients are completely dependent and approaching end of life. Score 9 (Terminally Ill) describes patients with a life expectancy under 6 months who are not otherwise overtly frail.

A CFS of 5 or higher is generally considered the threshold for frailty and carries important prognostic implications. Frail patients have higher mortality, longer hospital stays, greater risk of complications after surgery, higher ICU mortality, and are more likely to be discharged to institutional care rather than home.

Use the Clinical Frailty Scale as part of the assessment of any older adult (typically 65 years and older) in clinical settings where frailty status may influence treatment decisions. It is particularly valuable in the following scenarios: ICU admission decisions, where CFS helps clinicians and families understand the likelihood of meaningful recovery; preoperative assessment, where frailty is an independent predictor of surgical complications and mortality that may tip the risk-benefit analysis; emergency department triage, where frailty influences disposition and intensity of care; and goals-of-care discussions, where the CFS provides a common language for describing the patient's baseline functional status.

The CFS gained significant prominence during the COVID-19 pandemic when it was adopted by NICE and other organizations as a tool for resource allocation decisions. It takes approximately 60 seconds to complete and does not require any special equipment or testing, making it practical for busy clinical settings. It should be scored based on the patient's baseline function approximately 2 weeks before the current illness, not their current acute presentation.

The CFS is a subjective clinical judgment tool and inter-rater reliability, while generally good, can vary depending on the assessor's experience and familiarity with the patient. It requires knowledge of the patient's baseline functional status, which may be difficult to ascertain in emergency settings where collateral history from family or caregivers is unavailable. Scoring based on the acute presentation rather than baseline function is a common error that artificially inflates the frailty assessment.

The scale was developed and validated primarily in older adult populations (65 years and older) and should not be applied to younger adults or those with stable long-term disabilities. A 35-year-old wheelchair user with spinal cord injury, for example, should not be scored on the CFS because their functional limitations reflect a specific disability rather than the accumulating deficits that define frailty.

The CFS provides a single summary score and does not identify specific contributors to frailty that might be modifiable. A comprehensive geriatric assessment (CGA) is needed to identify specific deficits (malnutrition, polypharmacy, depression, deconditioning) that can potentially be addressed through targeted interventions. The CFS is best used as a screening and communication tool, not as a substitute for thorough geriatric evaluation.