A. Schwenk et al., Assessment of intracellular water by whole body bioelectrical impedance and total body potassium in HIV-positive patients, CLIN NUTR, 19(2), 2000, pp. 109-113
.: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.