Estimation of total-body and limb muscle mass in hemodialysis patients by using multifrequency bioimpedance spectroscopy

BACKGROUND: Skeletal muscle mass can be measured noninvasively with magnetic resonance imaging (MRI), but this is time-consuming and expensive. OBJECTIVE: We evaluated the use of multifrequency bioimpedance spectroscopy (BIS) measurements of intracellular volume (ICV) to model total-body skeletal muscle mass (TBMM) and limb skeletal muscle mass in hemodialysis patients. DESIGN: TBMM was measured by MRI in 20 male and 18 female hemodialysis patients with a median (range) age of 54 y (33-73 y), weight of 78.9 kg (43.2-120 kg), and body mass index (BMI; in kg/m2) of 27.3 (19.4-46.6). We measured total body water (TBW) by using D2O dilution, extracellular volume (ECV) as bromide space, and ICV as TBW minus bromide space. Total body potassium (TBK) measured as 40K was used as an independent model of TBMM. BIS was used to measure whole-body TBW (ankle to wrist) and TBW in the arms and legs. BIS-estimated ICV was used to construct models to calculate limb muscle mass and TBMM. The latter was compared with models derived from isotopic methods. RESULTS: BIS yielded a model for TBMM TBMM = 9.52 + 0.331 x ICV + 2.77 (male) + 0.180 x weight (kg) - 0.133 x age] (R2 = 0.937, P < 0.0001) as precise as TBK-measured TBMM TBMM = 1.29 + 0.00453 x TBK (mEq) + 1.46 (male) + 0.144 x weight (kg) - 0.0565 x age] (R2 = 0.930, P < 0.0001) or isotopic methods. BIS models were also developed for measuring leg and arm muscle mass. CONCLUSION: BIS provides an estimate of TBMM that correlates well with isotopic methods in approximating values obtained by MRI and can be used to estimate limb muscle mass.