Estimation of Body Composition and Normal Fluid Status Using a Calf Bioimpedance Technique

The aims of this study in hemodialysis (HD) patients were: 1. To evaluate the relationship of calf bioimpedance with total body composition and fluid status as measured by gold standard methods. 2. To investigate the ability of calf normalized resistivity (CNR) to predict the normal fluid status (dry weight: DW) in a prospective study. In the body composition study (n = 41), fluid status (ECV(Br)/FFM(MRI)), muscle mass (MM(MRI)), and total adipose tissue (TAT(MRI)) were measured by dilution (D2O and Br) and MRI methods three hours prior to HD treatment. Calf extracellular and intracellular resistance, resistivity, and CNR were measured with a multi-frequency bioimpedance device (Hydra 4200). In the fluid status study (n = 32 with 429 measurements), a nonlinear model based on the differences in CNR between patients and healthy subjects was established to predict DW(cBIS) previously determined by a separate continuous calf bioimpedance spectroscopy (cBIS) method. CNR significantly correlated with a gold standard hydration marker (ECV(Br)/FFM(MRI)). Calf body composition models were highly correlated with MM(MRI) (R(2) = 0.85) and TAT(MRI) (R(2) = 0.85). DW(cBIS) prediction was validated with a CNR model in the degree of differences of 0.94 ± 0.18, 0.39 ± 0.7 and -0.02 ± 0.8 kg from DW(cBIS) when post HD fluid overload was 1.8 ± 1.2, 1.15 ± 0.8 and 0.54 ± 0.5 kg, respectively. These differences are not considered to be clinically significant.