Frailty in Focus

Key Points The clinical frailty scale has the strongest psychometric validity in kidney disease apart from the physical frailty phenotype. Existing frailty instruments have strong predictive validity for mortality and hospitalizations across kidney disease populations. Future work should test validity in younger adults, psychosocial and physiologic domains, and use of frailty instruments as screeners. Background Frailty is a multisystem syndrome of decreased physiologic reserve with high prevalence, early incidence, and prognostic significance in kidney disease. Apart from the physical frailty phenotype (PFP), less is known regarding psychometric properties of other instruments. We critically appraise the validity and reliability of frailty instruments across the kidney disease continuum, acknowledge limitations, and highlight knowledge gaps. Methods Following Preferred Reporting Items for Scoping Reviews guidelines, we searched PubMed, EMBASE, Cochrane, Cumulated Index in Nursing and Allied Health Literature, Web of Science, ClinicalTrials.gov, and PsycInfo from website inception through September 2024. Eligible studies applied a validated frailty instrument apart from the PFP to a kidney disease population. Results We identified 136 articles after screening 4048 initial results. The most commonly cited instruments were the clinical frailty scale (CFS; N =56); Fatigue, Resistance, Ambulation, Illnesses, and Loss of Weight Scale ( N =30); and Edmonton frail scale ( N =16). Most studies included adults receiving hemodialysis ( N =85) and with CKD ( N =39). Median age ranges were 53–83 years. Most frailty instruments demonstrated predictive validity for mortality and hospitalizations. Concurrent validity was most frequently demonstrated between frailty and older age, female sex, greater comorbidities, and lower albumin. Seven studies reported reliability. While some instruments were feasible (CFS, Fatigue, Resistance, Ambulation, Illnesses, and Loss of Weight scale), their measurement could result in higher frailty prevalence compared with the PFP. Existing instruments do not capture the full spectrum of psychosocial and physiologic domains of frailty. Conclusions The CFS demonstrates the strongest validity, apart from the PFP, although its use may result in higher measured frailty prevalence. Further research should test the feasibility of screening for frailty in clinical practice; the psychometric properties ( i.e ., responsiveness) of frailty instruments in younger adults, those with AKI, kidney transplant recipients, and those receiving conservative kidney management; and whether adding psychosocial and/or physiologic markers improves frailty measurement validity. Addressing these gaps will facilitate wider frailty measurement in kidney disease research and aid adoption into practice.