Bioimpedance And Dxa Total Body Water Estimations In The Elderly

Abstract

Bioimpedance techniques have the ability to estimate total body water (TBW) and include single frequency bioimpedance (BIA), bioimpedance spectroscopy (BIS), and multiple-frequency bioimpedance (MFBIA). In addition, dual-energy X-ray absorptiometry (DXA) can predict TBW by using fat-free mass and a constant hydration status of 0.737%. However, the validity of the aforementioned methods has not been established in a healthy elderly population. PURPOSE: Compare BIA, BIS, MFBIA, and DXA TBW estimations in elderly men and women to a criterion deuterium oxide (D2O) TBW measurement. METHODS: Thirty-four women and twenty-four men over the age of sixty-five participated in the study (71 +/5yr, 68.8 +/12.0kg, 167.0 +/8.5 cm). Subjects reported to the lab in a fasted state and provided a urine sample before ingesting approximately 11 grams of D2O. Four hours later the subjects provided another urine sample for the calculation of TBW using a standard isotope dilution method. During the four hour equilibration period the subjects had TBW measured using BIA, MFBIA, BIS, and DXA in no particular order. RESULTS: For men, all methods produced similar and high r values (0.890.95) as well as low standard error of the estimate (SEE) values (1.26-1.52 L) with BIA producing the only nonsignificant mean difference (0.29 L, p=0.31). The MFBIA produced the largest mean difference between D2O and over predicted TBW by 3.43 L. DXA and BIS also both significantly over predicted TBW with mean differences of 1.74 and 2.10 L respectively (p<0.001). For women, all methods produced nearly identical and high r values (0.90-0.91) as well as low standard error of the estimate (SEE) values (0.94-1.02 L). All methods significantly (p<0.001) over estimated TBW, but mean differences were low for DXA (0.92 L) and BIA (0.89 L) compared to BIS (2.37 L) and MFBIA (2.47 L). CONCLUSIONS: The added frequencies used in the MFBIA and the complex Cole models of the BIS did not increase the validity of TBW estimation in elderly men and women as the BIA outperform both devices and uses a single frequency of 50 kHz. However, all methods demonstrated high r values and low SEE values and have the potential to accurately estimate TBW in the current population. However, based on the current results the BIA method used in the current study resulted in the most valid estimations of TBW for elderly men and women compared to D2O.