Results of this study demonstrated that frailty at the initiation of dialysis was associated with mortality or hospitalization within two years. To the best of our knowledge, this is the first study demonstrating predictive validity of 9-point CFS assessed by nurses for relatively short-term prognosis in incident dialysis patients. We also found correlation between the CFS score based on the nurses’ subjective assessment and several objective laboratory parameters such as CRP, Alb, Cr, and BNP.
In our study, 28% of the patients were classified into the frailty group when judged by the criterion of mean CFS score >= 5. The frequency of frailty in dialysis patients varies among reports. It seems to depend on the assessment method and patient background. Chu et al. demonstrated that frailty as assessed by Physical Frailty Phenotype (Fried’s criteria) was present in 71.4% among older incident hemodialysis patients and 47.3% in younger ones.20 Alfaadhel et al. reported that frailty assessed using 7-point CFS existed in 26% of all incident hemodialysis patients7, which was compatible with our data.
Screening for frailty is important because frailty is associated with increased risk of hospitalization, mortality, and falls in individuals with chronic kidney disease.21 Increased frailty consequently engenders huge physical and mental burdens on patients. Alfaadhel et al. demonstrated that a higher CFS score at dialysis initiation was associated with higher mortality. Our findings are compatible with their results.7 CFS, easily can be assessed, may be a useful predictor of mortality in incident dialysis patients.
Although CFS is a subjective assessment tool for frailty based on the health-care providers’ judgment, it has been shown to have high inter-rater reliability.1 In this study, the categorization (CFS score is above 5 or not) was consistent in 133 (86%) cases. The 9-point CFS was apparently reliable with small inter-rater differences in the clinical assessment of incident dialysis patients. Additionally, we calculated and used the mean of CFS scores from the two nurses for analyses in this study. We believe that the mean of the CFS scores from two nurses, who take care of patients under consideration of their conditions and daily lives, might increase the reliability of the results.
The correlation between CFS scores based on the clinician’s subjective judgement and various objective markers such as Alb, CRP, and BNP might support the reliability of CFS in our cohort. Serum albumin, known as an independent risk factor of mortality as well as a nutritional marker in end-stage renal disease (ESRD) patients, has been reported to be lower in frail individuals than in healthy ones.15,22 The mean serum albumin level was low at 3.14±0.55 g/dl, which might reflect the condition of the patients, such as chronic malnutrition and exhaustive illness in ESRD patients. Frail patients often have comorbidities that can affect the inflammatory parameters.23 Aggravation of inflammation can lead to structural damage to physiologic organs such as musculoskeletal, hematological (anemia), cardiovascular, and endocrine systems.24 Consequently, it is not surprising that serum CRP was correlated significantly with the CFS score. Regarding BNP, it has been reported that elevated BNP (>= 100 pg/ml is significantly associated with frailty in the general elderly population (OR: 2.63, 95% confidence interval: 1.61–4.32).25 Although the reasons for correlation between BNP levels and CFS scores in our study was not clear, it might be mediated by fluid overload and the presence of CVD, both of which are often seen in ESRD patients.
Patients of the frailty group (mean CFS >=5) had less planned dialysis initiation and longer hospitalization periods than patients of the non-frailty group (mean CFS <5). Although the reasons for these differences remain unclear, missing the appropriate timing to start dialysis can lead to an urgent start of dialysis and prolonged hospitalization, which is undoubtedly a great physical and medical cost burden for frail patients. This study found that eGFR at dialysis initiation was significantly higher in the frailty group, suggesting that eGFR based on serum creatinine might not reflect renal function in frail patients because of a loss of muscle mass, and that factors other than renal function (such as comorbidities) might have influenced the decision to initiate dialysis. Therefore, it might be necessary to consider not only objective clinical parameters but also frailty assessments based on clinical judgments to make decisions about dialysis initiation.26
The present study had several limitations. First, we might not have investigated or collected sufficient data of unknown factors affecting the relation between frailty and prognosis. Second, based on the nature of retrospective studies, potential influences of prognostic information related to the CFS assessment was a concern. Therefore, the CFS evaluators made decisions based solely on information from the dialysis initiation period and were separated from the investigator for patient prognosis. Third, because this study was conducted at a single tertiary hospital, it remains unclear whether the results were generalizable or not. Fourth, clinicians might misclassify the severity of CFS based on limited descriptions included in medical chart information. We tried to reduce the misclassification of patients by calculating the mean of CFS from two dialysis nurses. Fifth, the change in CFS score before and after dialysis initiation was not investigated. Finally, cognitive function was not evaluated in this study although recognition of patients with dementia might help to adequate CFS classification. To address these limitations, a large and multicenter prospective cohort study with long-term follow-up must be undertaken as a future study.
In conclusion, results of this study demonstrated that frailty at the initiation of dialysis is related to death or hospitalization within two years. Used by nurses who are familiar with patient's living and physical conditions, CFS might become an effective tool for predicting the prognoses of incident dialysis patients.