Body fluid overload and bioelectrical impedance analysis in renal patients.

Using a new bivariate vectorial approach to the standard bioimpedance analysis (tetrapolar, 50-kHz frequency), we evaluated the performance of a graphical method for the identification of patients with fluid overload. Two hundred and seventeen adult Caucasian subjects were divided into four classification groups: 86 healthy control subjects, 55 patients with mild-to-terminal chronic renal failure in conservative treatment (15% with apparent edema), 36 patients with idiopathic nephrotic proteinuria (58% with apparent edema), and 40 obese subjects. We found a bioimpedance threshold for apparent edema on the lower pole of the sex-specific 75% tolerance ellipse (bivariate tolerance interval) of the healthy population. This innovative graphical method allows identification, monitoring and therapy planning of patients with fluid overload using direct bioimpedance measurements without any assumption on body composition.