Bioelectrical impedance analysis (BIA) was used to determine total body water (TBW) and lean body mass (LBM) in patients with renal failure. The body's electrical resistance (R) was measured by the voltage to current ratio, injecting an 800microA alternating current with a frequency of 50KHZ and detecting a voltage drop between the wrist and the ankle. Impedance index (Height2/Resistance) compared favorably with TBW measured by deuterium (D2O) dilution method as the reference, giving the correlation coefficient (r) of 0.966 and standard error estimation (SEE) of 2.71 liter. The index was compared with LBM determined by dual-energy x-ray absorptiometry (DEXA) as the reference, giving r of 0.970 and SEE of 3.00kg. The r of 0.985 and SEE of 2.15kg were found between the reference method. BIA appeared to have a somewhat lower accuracy than those of the reference method. However, it is a useful clinical tool for estimating body composition, because it is easy, rapid and non-invasive. The existing BIA method is based on an extremely simple conductor model of the body. The accuracy may be improved further, based on a more realistic model for the body.
Absorptiometry, Photon ; Ankle ; Body Composition ; Body Water* ; Deuterium ; Electric Impedance* ; Humans ; Renal Insufficiency* ; Wrist