Survey of Spanish nephrologists’ opinion on the applicability of Fried’s geriatric frailty criteria in patients with end-stage renal disease

Abstract

Background

Fried described fragility as a biological syndrome in the geriatric population with 5 criteria (exhaustion, unintentional weight loss, low physical activity, slow walking speed, and poor grip strength). This diagnostic method is the most commonly used in patients with ESRD. This study aimed to analyse the opinion of Spanish nephrologists about its applicability in ESRD.

Methods

A survey adapted from a Delphi used by the Johns Hopkins University School of Public Health was distributed among Spanish nephrologists, with their permission and collaboration, and with the support of the Spanish Society of Nephrology.

Results

Of the 179 respondents, 99.4% felt that frailty is prevalent in ESRD. Involuntary weight loss criterion was considered of little use by 12.5% and exhaustion by 12.6%, with consensus on the usefulness of the other three criteria. New criteria were proposed, including depression (23.5%), dependence (18.8%), cognitive impairment (16.5%), dialysis intolerance (14.1%), and malnutrition (11.8%). Intra-dialysis static pedals (74.9%) and prehabilitation in renal transplant candidates (83.1%) were considered beneficial.

Conclusions

Unintentional weight loss and exhaustion were the criteria considered least appropriate for defining frailty in patients with ESRD. Future studies would be desirable to assess the applicability of the proposed new criteria and the efficacy of intervention and prehabilitation measures.

Clinical trial number

Not applicable.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-026-04763-x.

Introduction

Frailty is a concept first defined by geriatricians in elderly patients. It consists of a biological syndrome in which the capacity to respond to stressful situations is reduced because of the wear and tear of different physiological systems. This leads to greater vulnerability and a worse vital prognosis, increasing the risk of mortality, institutionalisation, falls, and hospitalisation [1–4].

Recognising frail patients would be the first step in developing interventions to improve their prognosis. In this sense, Fried et al., based on this definition and previous research, identified a frailty phenotype in the geriatric population, according to which, to be considered a frail patient, they had to meet at least three of these five criteria: involuntary weight loss, slow gait, decreased physical activity, loss of strength and exhaustion [5]. These same authors validated this phenotype in the population over 65 years of age, demonstrating that, in patients characterised as frail by these criteria, mortality tripled after 7 years of follow-up compared to those who did not meet any of them.

It has been observed that the prevalence of frailty increases with advancing age, although the presence of comorbidity in the patient is also considered an aetiological factor for its development. Sarcopenia or loss of strength and muscle mass is a term that overlaps largely with that of frailty, being associated with advanced age [6], but also with chronic diseases such as cancer, heart failure, cirrhosis or chronic kidney disease (CKD). In these situations, catabolism associated with factors such as inflammation, anorexia or insulin resistance is accelerated, leading to sarcopenia and frailty [7].

Although there are different scales to assess frailty, Fried’s criteria have been used in most studies of CKD patients [8, 9]. Applying these criteria to these patients, it has been observed that the prevalence of frailty is very high in this population. Several studies confirm that it is around 35% in end-stage renal disease (ESRD) patients on haemodialysis [10–12], with prevalence as high as 73% in some cohorts [8]. Furthermore, it has been shown that frail ESRD patients on haemodialysis are at increased risk of mortality, hospitalisation and falls [10, 13].

However, there are doubts as to whether the phenotype validated by Fried in the geriatric population is the most appropriate for assessing patients with ESRD. These criteria could probably be modified to provide a tool that helps us better predict our patients’ risk status. It is also essential to specify the most favourable interventions that can improve prognosis and impact on the evolution of renal transplantation in candidate patients, since it is considered that prehabilitation, or a programme designed to improve functional capacity before transplant surgery, can improve the results of the intervention and the prognosis of these patients [14, 15].

In this regard, a study has been published that analyses the opinion of clinicians and patients regarding the usefulness of Fried’s frailty criteria in patients with ESRD [16]. Adapting the questionnaire used in this publication, developed by the Johns Hopkins University School of Public Health, and with their permission and collaboration, we have surveyed nephrologists in our country to find out their opinion on the concept of frailty in patients with ESRD, and the possible implementation of intervention measures to prevent or reverse this syndrome. In this way, we hope to come closer to what could be a more appropriate definition of frailty in this specific group of patients to be able to implement appropriate intervention measures and to predict the risk involved more accurately, a beneficial aspect in clinical decision-making.

Methods

With the collaboration of the Spanish Society of Nephrology, a survey was disseminated to ascertain the opinion of nephrology specialists regarding frailty in the ESRD population (Additional file 1: Survey). This survey was adapted from a Delphi previously used [16], with the permission and collaboration of the Johns Hopkins University School of Public Health, to assess the usefulness of the Fried criteria in patients with ESRD. The survey consisted of 34 questions combining different aspects related to frailty and its characteristics. The questions were divided into five blocks: introduction, frailty, asthenia, interventions, and prehabilitation (Table 1). The Delphi questions were answered by members of the Spanish Society of Nephrology, and their anonymity was always preserved.

Table 1.

Blocks of questions for the survey

Blocks	Content
Introduction	Respondent characteristics
Frailty	Views on frailty prevalence and criterion validity in ESRD
Asthenia	Definition, intensity, persistence and causes in nephrological patients
Interventions	Applicability, benefit and category of possible intervention measures
Prehabilitation	Appropriateness and applicability of a programme designed to improve functional capacity in patients who are candidates for renal transplantation before surgery

Statistical analysis was conducted using IBM SPSS Statistics 26.00 (IBM Corp, Armonk, NY, USA), and the results were compared using descriptive statistics for categorical variables with frequency analysis. Opinion and free-response questions were analysed independently to classify them. Consensus was defined as an agreement of more than 90%.

Result

A total of 179 nephrology specialists responded to the survey. Of these, 107 (59.8%) were female and 109 (60.9%) had more than 15 years of clinical practice. Of the respondents, 178 (99.4%) considered frailty to be a more prevalent condition in ESRD patients than in the general population. Opinions on the applicability of each of the frailty criteria proposed by Fried et al. in patients with ESRD are reflected in Fig. 1A, with consensus on their usefulness (over 90% agreement) for three of the five criteria. Figure 1B describes new criteria that respondents felt might be more appropriate for diagnosing frailty in patients with ESRD. For the 2 Fried criteria for which there was no consensus on their usefulness for diagnosing frailty in these patients, the reasons why they were considered less accurate are presented in Table 2.

Fig. 1.

Applicability of Fried’s criteria in ESRD patients. Percentage of affirmative responses regarding the validity of Fried’s criteria (A) and the new proposed frailty criteria for ESRD patients (B)

Table 2.

Rationale for eliminating non-consensus frailty criteria in ESRD patients on Dialysis

Reasons for eliminating “exhaustion” (21 respondents)	n (%)
Exhaustion may be due to anaemia.	11 (52.4)
Exhaustion may be due to uraemia, inadequate dialysis	10 (47.6)

Reasons for eliminating “Unintentional weight loss” (18 respondents)	n (%)
Weight may depend on fluctuations in blood volume.	7 (38.9)
Weight may depend on uraemia, due to inadequate dialysis.	7 (38.9)
Weight may depend on intercurrent comorbidities (infection, neoplasia).	4 (22.2)

Opinions regarding interventions to prevent and improve frailty and the usefulness of performing a prehabilitation programme before renal transplant surgery are reflected in Table 3. As described in the latter table, some respondents considered the performance of mental agility exercises during the dialysis session inadequate. Of those who gave a negative response, 6 explained the reasons for this response: decreased brain flow during procedure 4 (66.7%), and lack of solid evidence to carry out this intervention 2(33.3%). Concerning the refusal to consider the use of stationary pedals during dialysis as a practical measure, the reasons given by the 16 respondents who proposed a justification were: it would not be the best time 11(68.8%), lack of interest of the patients 4(25%), or that this intervention would be insufficient to improve the physical capacity of the patients 1(6.3%). When asked which interventions would be most useful to prepare patients for renal transplant surgery (prehabilitation), the opinions were: an exercise programme 36(48.6%), care by a multidisciplinary team with physical trainer, psychologist, nutritionist and social worker 13(17.6%), psychological care 11(14.9%), and nutritional intervention 14(18.9%).

Table 3.

Nephrologists’ views on possible interventions to prevent and reverse frailty in patients with ESRD on Dialysis and prehabilitation in patients who are candidates for kidney transplantation

Nephrologists’ views on interventions in ESRD patients on dialysis	Yes n (%)	No n (%)	Don’t know n (%)
Cognitive function may be preserved with mental agility exercises during dialysis	112 (62.9)	4 (2.2)	62 (34.8)
They would be interested in mental agility exercises during dialysis.	84 (47.2)	6 (3.4)	88 (49.4)
They could improve their physical function by using stationary pedals during dialysis.	134 (74.9)	13 (7.3)	32 (17.9)
They would be interested in using stationary pedals during dialysis.	83 (46.9)	21 (11.9)	73 (41.2)
A prehabilitation programme could improve kidney transplant outcomes	148 (83.1)	2 (1.1)	28 (15.7)
A prehabilitation programme could reduce frailty after kidney transplantation	146 (83)	3 (1.7)	27 (15.3)
They would be interested in a prehabilitation programme before kidney transplantation.	139 (79)	1 (0.6)	36 (20.5)

Discussion

In order to contextualizing the findings of this study and facilitating implementation in other countries, we provide a brief analysis of Spain’s position within a global framework. The International Society of Nephrology reports a prevalence of 13.7 nephrologists per million population in this country, an estimate that coincides with international workforce benchmarking [17]. According to the Spanish Dialysis and Transplant Registry [18], in 2024 the mortality rate for haemodialysis patients was 13.4%, for peritoneal dialysis patients 9,1% and for transplant recipients 2.9%. These annual mortality rates are similar in developed European countries, being higher in dialysis patients (up to 14.4% per year) and lower in transplant recipients (around 2.2% per year) [19].The age distribution of patients undergoing renal replacement therapy in Spain in 2024 was as follows: 26% >75 years old, 25% 65–74 years old, 38% 45–64 years old and 11% 15–44 years old. Based on the Global Observatory on Donation and Transplantation, the kidney transplantation rate was among the highest in Europe, with a rate of 83.2 kidney transplants per million population [20].

Most of the nephrologists surveyed in this study had more than 15 years of clinical practice, translating into extensive knowledge of the characteristics of patients with ESRD. Regarding the opinions of the respondents, almost all of them considered that frailty is a more prevalent condition in renal patients than in the general population, thus justifying the importance of this study and the need to more precisely define the diagnostic criteria for frailty, adjusted to the characteristics of the ESRD population.

As in the survey published by the Johns Hopkins University School of Public Health group [16], there is practical unanimity regarding the applicability of low physical activity as a marker of frailty in patients with ESRD, and agreement was also found on the cost-effectiveness of measuring grip strength and assessing gait speed for its diagnosis, which could be considered suitable for application in our patients, as well as in the geriatric population. However, there was no consensus on the usefulness of exhaustion and unintentional weight loss criteria. The reasons given for not applying the criteria of exhaustion in ESRD patients were that this symptom is associated with anaemia and uraemia, two conditions inherent to ESRD, potentially correctable with pharmacological treatment and adequate dialysis. In this population, it may be challenging to determine whether exhaustion is conditioned by anaemia or uraemia or is part of the frailty syndrome itself. In addition, poor tolerance to dialysis, with episodes of hypotension, could contribute to worsening asthenia, so this could also be a precipitating factor for this criterion. As for the justifications for why the criterion of unintentional weight loss would not be valid, it was first argued that changes in this measurement parameter are conditioned by fluctuations in blood volume in patients on dialysis. This opinion coincides with that of clinicians and patients in the Delphi study published by the Johns Hopkins School of Public Health group [16]. In addition, it was considered that weight loss may also be associated with uraemia itself, and with other relatively frequent comorbidities in these patients, such as infections and neoplasms. Concerning uraemia, we know that retention of uraemic toxins leads to a proinflammatory state, with increased oxidative stress and a tendency to metabolic acidosis, circumstances related to loss of appetite and consequent weight loss, which could be alleviated with adequate dialysis. Many studies relate these alterations in CKD patients to frailty, considered aetiological agents of frailty [14, 21]. Fried also hypothesises in her research that comorbidities such as cancer could be a cause of frailty, and that frailty predisposes to disability or dependence in the future [5]. Other scales, such as the Frailty Index, include factors such as comorbidity and dependence among their criteria, considering that frailty is conditioned by these factors [22].

However, it would be worth considering whether it is correct to ignore two potentially correctable frailty criteria defined by Fried (exhaustion and involuntary weight loss). It would be interesting to conduct a second round of the Delphi survey in future to explore their meaning and possible corrective measures in greater depth, and to determine whether correcting these factors through better care would change patients’ and physicians’ perceptions of exhaustion and involuntary weight loss. Knowing that these factors are essential in determining frailty among ESRD patients would provide a stimulus for intervention.

Regarding new criteria that could be applied to patients with ESRD, the following were the most frequently proposed: depression or isolation, dependence, cognitive impairment, dialysis intolerance and malnutrition. Depressed mood was the most commonly proposed criterion. Although other scales also have this criterion [22], it is not one of the most widely used. However, among the interventions recommended for the prehabilitation of renal transplant candidates, psychological care is considered, with psycho-social and psycho-educational measures to improve depression and anxiety [23], so identifying vulnerable patients in this sense could be of interest to consider possible interventions. The second criterion proposed was dependence. As mentioned above, dependence is considered by Fried et al. to be a consequence of frailty. However, other authors consider it a criterion within their measurement scale [22, 24]. Cognitive impairment, proposed in third place, is associated with frailty in incident haemodialysis patients [25]. Although it is not part of Fried’s criteria, many other frailty scales also have this criterion [22, 26]. Intolerance to dialysis would be a specific measurement criterion for this type of patient, which could be of interest, since difficulties with dialysis treatment may cloud the prognosis, condition uraemia and greater retention of proinflammatory toxins, indirectly leading to other less specific symptomatology, such as asthenia and weight loss. Finally, the last of the most frequently proposed new criteria was malnutrition. This criterion could have a clear relationship with unintentional weight loss, and measures to improve the nutritional status of frail patients have also been proposed to prevent or reverse this syndrome [23]. In the first published Delphi [16], from which this survey is derived, clinicians identified some of the criteria proposed in this paper as the most relevant new criteria, thus emphasising their importance in conceptualising frailty in the nephrology community. These criteria were history of falls and physical impairment (which could be identified with what we have termed dependency or disability in this survey), cognitive impairment and malnutrition.

Also, in line with the first published Delphi [16], most respondents felt that intra-dialysis static pedals would help preserve the physical capacity of dialysis patients and that patients would be interested in this. The percentage of agreement was higher regarding the usefulness of a prehabilitation programme to improve renal transplant outcomes, frailty after renal transplantation and the perception that patients would be interested in prehabilitation. The measures proposed by the respondents to design a prehabilitation programme were physical activity exercises, psychological care, implementation of a nutrition programme, and patient assessment from a multidisciplinary point of view. These interventions coincide with the recommendations formulated by the “Prehabilitation in Solid Organ Transplant Candidates” working group of the European Society of Organ Transplantation [23], which, given the growing need for a clinical practice guideline, has drawn up recommendations based on the available evidence. These recommendations are based on implementing a multimodal programme, with physical, psychosocial and nutritional training interventions. In the future, it would be interesting to propose a new round of questions about what type of intervention might be most appropriate on a practical level to improve mental agility, physical condition and nutritional status. For example, it would be interesting to determine whether patients would be more receptive to pedal exercise during dialysis or to a supervised exercise programme at home. In addition, the European Society of Organ Transplantation stress the importance of developing new clinical trials to assess the feasibility and efficacy of a multimodal prehabilitation programme, such as the FRAIL-MAR study (NCT04701398) [27], which is under development. Preliminary results from this clinical trial suggest that an exercise-based prehabilitation programme in candidates for kidney transplantation improves muscle strength and exercise capacity, even in frail patients [28]. Long-term results and other outcomes specified in the trial protocol are pending publication.

One limitation of this study was that it only reflects the views of nephrologists who treat patients with ESRD and not those of other specialists, such as nutritionists or geriatricians. Although nephrologists have more knowledge about aspects related to CKD, their view may be limited in other aspects. Furthermore, the survey was conducted in a single country and may not be generalisable to other regions. In this regard, it should be noted that the results were fairly consistent with those obtained at Johns Hopkins [16].

Conclusions

There is a broad consensus that frailty is a prevalent condition in ESRD patients. Among Fried’s frailty criteria, the least appropriate to characterise ESRD patients would be unintentional weight loss and exhaustion. New frailty criteria are proposed for these patients, such as depression, dependence, cognitive impairment, dialysis intolerance and malnutrition. Most respondents agree to implement intervention and prehabilitation measures to prevent or reverse frailty. Further studies are needed to determine the validity of the new criteria and assess the effectiveness of the different interventions and prehabilitation measures.

Supplementary Information

Below is the link to the electronic supplementary material.

Abbreviations

CKD

Chronic kidney disease

ESRD

End-stage renal disease

Author contributions

MPF, PMM, DRP and MAMD contributed to conception and design of the article. MPF, PMM, AAF, SLO and DRP contributed to analysis of the data and drafting of the article. PMM, DRP and FTM contributed to the interpretation of data and revision of the article. All authors read and approved the final manuscript.

Funding

This research did not receive funding.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The survey did not include patient data, just doctors’ opinions, it was completely anonymous, and informed consent was implicit in the heading of the own survey. For this reason, review by a research ethics committee was not requested as there were no relevant ethical issues to address, including those concerning data protection (Regulation EU 2016/679 of the European Parliament and of the Council of 27 April 2016). This study adheres to the Declaration of Helsinki.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.