Objective: To address whether: (1) bioelectrical impedance analysis (BIA) can provide precise and accurate estimates of total body water (TBW) and extracellular water (ECW) in healthy elderly subjects, that display age-induced changes in body composition, (2) BIA models are improved by introducing variables related to geometrical body-shape and osmolarity.
Design: Cross-validation of available BIA models and models developed in the study.
Subjects: 58 healthy elderly subjects (31 women, 27 men, 66.8+/-4.7 y, mean +/- s.d.)
Measurements: BIA at 5, 50 and 100 kHz, 18O labelled water measurements of TBW, Br measurements of ECW, anthropometric variables, plasma osmolarity.
Results: Published BIA models for estimating TBW, entail various degrees of bias. Precise models (SEE of the models 0.8 L at 100 kHz, 1.0 L at 50 kHz) involving height2/resistance, weight, gender, circumferences and plasma osmolarity were established with data from 30 subjects chosen at random. Cross-validation of an independent group (n = 28) showed no bias (-1.5+/-3.2 L at 100 kHz, -1.4+/-3.2 L at 50 kHz, P = NS).
Conclusion: We conclude that BIA models with increased accuracy and precision for predicting ECW and TBW can be derived in healthy elderly subjects. Repeated measures had a mean difference of 0.2+/-1.2 L.