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Multi-frequency bioelectrical impedance for assessing total body water and extracellular water in elderly subjects
M Visser1, P Deurenberg, W A van Staveren
1Department of Human Nutrition, Wageningen Agricultural University, The Netherlands.
Objective:
The objective of this study was to investigate the utility of multifrequency bioelectrical impedance for the estimation of total body water (TBW) and extracellular water (ECW) in an elderly population.
Design:
Body impedance at 8 frequencies (1-1350 kHz) was measured in duplicate within 1 week. TBW and ECW were determined using deuterium oxide and potassium bromide dilution respectively.
Setting:
At the Department of Human Nutrition.
Subjects:
81 women and 36 men, aged 63-87 years, volunteered as subjects.
Results:
Application of prediction equations from the literature, which are mostly based on impedance measurements in young and middle-aged subjects, resulted in large prediction errors of TBW and ECW which were related to the water distribution of the body. New sex-specific prediction equations for the estimation of TBW and ECW were developed for the elderly population and internally validated in random sub-groups. TBW and ECW were best predicted using impedance at frequencies of 5 and 50 kHz respectively, and by using body weight. Prediction errors for TBW were 3.1 kg (7.3%) and 2.7 kg (8.5%) and for ECW 2.2 kg (12.3%) and 1.0 kg (7.4%) for men and women respectively.
Conclusions:
Multi-frequency impedance measurements are useful to assess TBW and ECW in groups of elderly subjects. However, the prediction errors are larger compared to young and middle-aged subjects, and are related to body water distribution. Individual errors are sometimes unacceptably large.