Bioelectrical impedance analysis measurements of total body water and extracellular water in healthy elderly subjects

Abstract

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.