MEASUREMENT OF TOTAL-BODY WATER BY BIOELECTRICAL-IMPEDANCE IN CHRONIC-RENAL-FAILURE

Objective: Abnormalities of body hydration are common in patients with advanced chronic renal failure (CRF) and may be associated with impor tant adverse clinical effects, even in the absence of clinical feature s of fluid retention or depletion. Bioelectrical impedance analysis (B IA) is a simple, non-invasive method of measuring body water content a nd thus could be of use in the management and study of patients with C RF. This study was performed to assess the ability of BIA to measure t otal body water (TBW) in patients with CRF. Design: TBW was measured b y two different impedance systems, with comparison of the results with TBW determined by deuterium oxide dilution (D2O). Setting: Renal Unit , Leeds General Infirmary and Centre for Bone and Body Composition Res earch, University of Leeds, UK. Results: The range of the 95% limits o f method agreement between BIA and D2O expressed as a percentage of th e 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 limit s were moderately greater than controls at +/-17.3% (RJL) and +/-21.9% (Holtain). Analysis of subgroups of the CRF patients showed the small est 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%). Conclusions: BIA is less accurate for the measurement of TBW in patients with CRF than in healthy subjects, though in some groups o f patients the effect of CRF on the validity of this technique may be only mild. Abnormalities of reactance suggest that abnormal variabilit y in the distribution of fluid between intra- and extracellular compar tments is the major cause of reduced accuracy of TBW calculated by BIA in CRF patients.