Background: Frail older adults experience higher rates of adverse health outcomes. Therefore, assessing pre-hospital frailty early in the course of care is essential to identify the most vulnerable patients and determine their risk of deterioration. The Clinical Frailty Scale (CFS) is a frailty assessment tool that evaluates pre-hospital mobility, energy, physical activity, and function to generate a score that ranges from very fit to terminally ill.

Purpose: To synthesize the evidence of the association between the CFS degree and all-cause mortality, all-cause readmission, length of hospital stay, adverse discharge destination, and functional decline in patients >65 years in acute clinical settings.

Design: Systematic review with narrative synthesis.

Methods: Electronic databases (PubMed, EMBASE, CINAHL, Scopus) were searched for prospective or retrospective studies reporting a relationship between pre-hospital frailty according to the CFS and the outcomes of interest from database inception to April 2020.

Results: Our search yielded 756 articles, of which 29 studies were included in this review (15 were at moderate risk and 14 at low risk of bias). The included studies represented 26 cohorts from 25 countries (N = 44166) published between 2011 and 2020. All included studies showed that pre-hospital frailty according to the CFS is an independent predictor of all adverse health outcomes included in the review.

Conclusion: A primary purpose of the CFS is to grade clinically increased risk (i.e. risk stratification). Our results report the accumulated knowledge on the risk-predictive performance of the CFS and highlight the importance of routinely including frailty assessments, such as the CFS, to estimate biological age, improve risk assessments, and assist clinical decision-making in older adults in acute care. Further research into the potential of the CFS and whether implementing the CFS in routine practice will improve care and patients' quality of life is warranted.