Bioimpedance spectroscopy for the estimation of fat-free mass in end-stage renal disease

Background & aims: Bioimpedance spectroscopy may provide reliable estimates of fat-free mass in end-stage renal disease patients. We aimed to evaluate the ability of bioimpedance spectroscopy to estimate fat-free mass in end-stage renal disease patients using dual-energy X-ray absorptiometry as a reference. Methods: Fat-free mass measured by bioimpedance spectroscopy was compared to fat-free mass measured by dual-energy X-ray absorptiometry in 16 end-stage renal disease patients on hemodialysis, 12 undialysed end-stage renal disease patients and 23 control subjects. Results: Methods were highly correlated for fat-free mass in all subject groups (r= 0.87, P< 0.001). Mean bioimpedance spectroscopy measures of fat-free mass were not different from the dual-energy X-ray absorptiometry measures in any subject group. Individual comparisons revealed wide limits of agreement between methods in hemodialysis (11.6 to -9.72. kg) and undialysed patients (10.95 to -14.73. kg). Conclusions: Although bioimpedance spectroscopy estimates of fat-free mass in the end-stage renal disease patient groups were not different from dual-energy X-ray absorptiometry and the methods were highly correlated, there was great individual variability. From these data it is clear that future studies are warranted before bioimpedance spectroscopy can be recommended as a valid clinical tool for assessing fat-free mass in end-stage renal disease patients.