Abstract
Body composition was measured in 112 surgical patients and eight normal subjects by bioelectrical impedance analysis (BIA), and the results compared with our standard five-compartment method utilizing in vivo neutron activation analysis and tritium dilution space to measure fat-free mass and total body water. In a population with a mean fat-free mass of 49.2 kg by the latter method, BIA underestimated fat-free mass by 1.3 kg, with a standard deviation (SD) of 4.0 kg. Total body water was overestimated by 0.5 liter, with SD of 0.47 liter, when compared to a mean tritium dilution space of 36.7 liter. Changes in total body water which occurred over a treatment period of at least 1 week were also measured by the two methods. The change as measured by isotopic dilution could be estimated from the change as measured by BIA with a standard error of 2.25 liter. Although the results suggest that BIA should not be used as a research tool, it is concluded that in clinical practice, when nutrient requirements are being estimated, fat-free mass measured by BIA may have a useful place.
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