Novel prediction equations for appendicular skeletal muscle mass in hemodialysis patients: referenced against bioelectrical impedance analysis.

BACKGROUND

Accurate assessment of appendicular skeletal muscle mass (ASM) is essential in clinical practice and research involving patients undergoing hemodialysis (HD). However, ASM prediction equations developed in the general population may be inappropriate for HD patients because of dialysis-related alterations in body composition and hydration status.

OBJECTIVE

To evaluate the performance of existing anthropometric ASM prediction equations in HD patients and to develop dialysis-specific equations tailored to this population.

METHODS

In this cross-sectional study, 111 patients receiving maintenance hemodialysis were enrolled. ASM was measured using multi-frequency bioelectrical impedance analysis (BIA) under standardized post-dialysis conditions. The performance of three previously published equations, namely the height-weight (HW), limb-length-circumference (LC), and height-circumference (HC) models, was assessed. New dialysis-specific equations were developed using anthropometric variables through linear regression. Agreement was evaluated using Bland-Altman analysis, and internal validation was performed using cross-validation and bootstrap resampling.

RESULTS

Existing equations demonstrated limited agreement with BIA-measured ASM, showing substantial systematic bias and wide limits of agreement. Two dialysis-specific equations were developed: an advanced HW model (adjusted R2 = 0.785, RMSE = 2.712 kg) and a HW plus HC (HH) model (adjusted R2 = 0.807, RMSE = 2.628 kg). Both models showed markedly improved agreement with minimal bias and narrower limits of agreement compared with the original equations. Internal validation revealed more stable performance of the HH model, which maintained consistent agreement across internal validation and ultrafiltration-stratified sensitivity analyses.

CONCLUSION

ASM prediction equations derived from the general population have limited applicability in patients undergoing maintenance hemodialysis. Dialysis-specific anthropometric calibration improves agreement with reference ASM, with the HH equation providing a practical and reliable tool for muscle mass assessment in this population.