#287 Effective muscle index based on muscle mass and quality to diagnose sarcopenia and predict renal survival in CKD patients

Abstract Background and Aims Sarcopenia is highly prevalent in CKD patients due to specific pathophysiologies such as chronic inflammation and uremic toxin accumulation, and is strongly associated with renal dysfunction and poor prognosis. Muscle quality, which reflects myofiber density and myocyte condition, has been recently recognized as an important factor to assess sarcopenia as well as muscle mass. Worsened muscle quality is associated with poor physical performance and renal prognosis. Therefore, it is desired to diagnose sarcopenia based on both muscle mass and quality. However, no definite criterion, which include muscle quality, has been proposed to assess sarcopenia. We recently developed effective muscle index (EMI), an index that reflects both muscle mass and muscle quality, to accurately assess sarcopenia. The aim of this study is to evaluate the feasibility of EMI to assess sarcopenia and renal prognosis. Method We conducted a single-center, prospective study. This study included 116 patients with CKD who underwent blood tests and bioelectrical impedance analysis between April 2021 and October 2022. Muscle mass was assessed by appendicular skeletal muscle mass (ASM) and skeletal muscle mass index (SMI), calculated from ASM divided by height. Muscle quality was assessed by phase angle (PhA) using MC-780A-N (TANITA, Tokyo, Japan). Sarcopenia was determined by grip strength (HGS) and SMI based on the EWGSOP2 algorithm. The respective cutoff values were set according to the AWGS 2019 sarcopenia diagnostic criteria. EMI was calculated as ASM × PhA. Correlations of HGS to age, eGFR, body mass index (BMI), SMI, ASM, PhA, and EMI were analyzed using Pearson's correlation coefficient. Influencing factors for HGS were determined using multiple linear regression analysis that include age, sex, eGFR, BMI, SMI, and EMI as explanatory variables. In addition, a cutoff value of EMI to diagnose sarcopenia was determined. Patients were further classified into high and low EMI groups, and renal prognoses were compared. The surrogate endpoint of renal function was defined as a 30% decrease in eGFR or initiation of dialysis. Renal survival was assessed by the Kaplan-Meier analysis and the Cox proportional hazards model. Results Included patients were 57.8% male, 64.2 ± 16.9 years old, and eGFR 39.69 ± 27.7 mL/min/1.73 m2. CKD stages of the subjects were G1–2 19.0%, G3a 19.8%, G3b 22.4%, G4 19.0%, G5 19.8%, respectively. HGS correlated with age, eGFR, BMI, SMI, ASM, PhA, and EMI (age; r = 0.501 and P < 0.001, eGFR; r = 0.331 and P < 0.001, BMI; r = 0.361 and P < 0.001, SMI; r = 0.777 and P < 0.001, ASM; r = 0.843 and P < 0.001, PhA; r = 0.679 and P < 0.001, and EMI; r = 0.856 and P < 0.001). Multiple linear regression analysis showed that EMI independently affected HGS (age; Stdβ = −0.059 and P = 0.398, sex; Stdβ = 0.196 and P = 0.004, eGFR; Stdβ = 0.056 and P = 0.378, BMI; Stdβ = −0.174 and P = 0.799, SMI; Stdβ = 0.160 and P = 0.252, and EMI; Stdβ = 0.554 and P < 0.001). The receiver operating characteristic (ROC) curve of EMI for sarcopenia diagnosis showed an area under the curve of 0.976/0.975 (male/female, respectively). The cut-off value of EMI was determined at 87.7/47.5 with a sensitivity of 89.8/91.9% and a specificity of 100/100% (male/female, respectively) (Fig. 1). The renal survival rate was significantly lower in patients with low EMI (P < 0.001) (median follow-up 545 days) (Fig. 2). Multivariate Cox proportional hazards regression analysis adjusted for age, sex, BMI and eGFR revealed that low EMI was an independent predictor of CKD progression (Hr = 3.54, 95% CI = 1.06–11.83, and P < 0.001). Conclusion This study demonstrated the following: (1) EMI is the novel diagnostic marker for sarcopenia that reflects muscle mass and quality. (2) Sarcopenia can be simply assessed by EMI without measuring muscle strength. (3) EMI is a prognostic factor for renal progression in CKD patients.