Measurement of total body water by bioelectrical impedance in chronic renal failure

Abnormalities of body hydration are common in patients with advanced chronic renal failure (CRF) and may be associated with important adverse clinical effects, even in the absence of clinical features of fluid retention or depletion. Bioelectrical impedance analysis (BIA) is a simple, non-invasive method of measuring body water content and thus could be of use in the management and study of patients with CRF. This study was performed to assess the ability of BIA to measure total body water (TBW) in patients with CRF.

TBW was measured by two different impedance systems, with comparison of the results with TBW determined by deuterium oxide dilution (D2O).

Renal Unit, Leeds General Infirmary and Centre for Bone and Body Composition Research, University of Leeds, UK.

The range of the 95% limits of method agreement between BIA and D2O expressed as a percentage of the mean for the group was +/- 13.4% for the RJL 101A system and +/- 15.6% for the Holtain system in controls. For the whole CRF group the limits were moderately greater than controls at +/- 17.3% (RJL) and +/- 21.9% (Holtain). Analysis of subgroups of the CRF patients showed the smallest limits in those receiving peritoneal dialysis (+/- 15.5% RJL and 18.2% Holtain). Limits were greater for patients on haemodialysis (+/- 16.0% RJL and +/- 23.8% Holtain) and undialysed patients (+/- 20.1% and +/- 23.0%).

BIA is less accurate for the measurement of TBW in patients with CRF than in healthy subjects, though in some groups of patients the effect of CRF on the validity of this technique may be only mild. Abnormalities of reactance suggest that abnormal variability in the distribution of fluid between intra- and extracellular compartments is the major cause of reduced accuracy of TBW calculated by BIA in CRF patients.