The role of fat-free mass index in evaluating protein-energy wasting in maintenance hemodialysis patients: a multicenter cross-sectional study

Objective Protein-energy wasting (PEW) is prevalent in maintenance hemodialysis (MHD) patients and associated with poor outcomes. This study aimed to evaluate the agreement of fat-free mass index (FFMI) measured by bioelectrical impedance analysis (BIA) with conventional nutritional tools and to explore its potential value as a supplementary screening measure for PEW in MHD patients. Methods In this multicenter cross-sectional study, 272 MHD patients were enrolled between April 2016 and October 2019. Body composition was assessed using a multifrequency BIA device capable of segmental and whole-body composition analysis. Patients were classified into low or normal FFMI groups based on established sex-specific criteria (FFMI 17 kg/m 2 for men and 15 kg/m 2 for women). Nutritional status was further evaluated using serum albumin (ALB), body mass index (BMI), Nutritional Risk Screening 2002 (NRS2002), and the Seven-Point Subjective Global Assessment (7-point SGA). Correlation and agreement analyses were performed between FFMI and other nutritional parameters. Results The mean age of participants was 58.8 ± 12.7 years, with a mean FFMI of 16.6 ± 2.2 kg/m 2 . The prevalence of low FFMI was 38.6%. FFMI demonstrated a non-linear relationship with age, peaking in the 41–50 age group. It was positively correlated with body weight ( r = 0.71, p 0.01), BMI ( r = 0.59, p 0.01), mid-arm circumference (MAC, r = 0.55, p 0.01), mid-arm muscle circumference (MAMC, r = 0.52, p 0.01), and handgrip strength (HGS, r = 0.24, p 0.01). Notably, FFMI identified a significant proportion of patients with low muscle mass who were classified as normal by ALB (38.7%), BMI (31.4%), NRS2002 (23.4%), and 7-point SGA (20.0%). The McNemar test and consistency analysis revealed fair to moderate agreement between FFMI and BMI, NRS 2002, and the 7-point SGA ( p 0.01). Conclusion Conventional nutritional assessment tools, including ALB, BMI, NRS2002, and SGA, frequently fail to detect low muscle mass in MHD patients. FFMI derived from BIA provides an objective, non-invasive, and potentially useful measure that may aid in the screening of PEW, particularly in detecting low muscle mass that is often missed by conventional tools. We recommend the integration of BIA-based body composition analysis as a supplementary tool into routine nutritional management of hemodialysis patients to enable timely interventions.