Assessment of intracellular water by whole body bioelectrical impedance and total body potassium in HIV-positive patients

.:Abstract-Objective: Bioelectrical impedance analysis (BIA) is widely used as bedside assessment of body composition. Body cell mass (BCM) and intrac ellular water (ICW) are clinically important body compartments. Estimates o f ICW obtained from BIA by different calculation approaches were compared t o a reference method in male HIV-infected patients. Patients: Representative subsample of clinically stable HIV-infected outpat ients, consisting of 42 men with a body mass index of 22.4 +/- 3.8 kg/m(2) (range, 13-31 kg/m(2)). Methods: Total body potassium was assessed in a whole body counter, and com pared to 50 kHz mono-frequency BIA and multifrequency bioelectrical impedan ce spectroscopy. Six different prediction equations for ICW from BIA data w ere applied. Methods were compared by the Bland-Altman method. Results: BIA-derived ICW estimates explained 58% to 73% of the observed var iance in ICW (TBK), but limits of confidence were wide (-16.6 to +18.2% for the best method). BIA overestimated low ICW (TBK) and underestimated high ICW (TBK) when normalized for weight or height. Mono- and multifrequency BI A were not different in precision but population-specific equations tended to narrower confidence limits. Conclusion: BIA is an unreliable method to estimate ICW in this population, in contrast to the better established estimation of total body water and e xtracellular water. Potassium depletion in severe malnutrition may contribu te to this finding but a major part of the residual between methods remains unexplained. (C) 2000 Harcourt Publishers Ltd.