Estimation of fluid volumes in hemodialysis patients: comparing bioimpedance with isotopic and dilution methods.

Both single-frequency bioimpedance and multiple-frequency spectroscopy are equally accurate in measuring total-body water and intracellular fluid. Estimates are consistent at a population level but not at the individual level, because of wide limits of agreement. There is no real 'gold standard' method providing estimates with absolute accuracy (in liters). Bioelectrical impedance vector analysis allows comparison of the actual body impedance with that of the reference population (in Ω/m). Hemodialysis prescription can be optimized with the use of this feedback.