Mean Expected Error in Prediction of Total Body Water: A True Accuracy Comparison between Bioimpedance Spectroscopy and Single Frequency Regression Equations

Abstract

For several decades electrical bioimpedance (EBI) has been used to assess body fluid distribution and body composition. Despite the development of several different approaches for assessing total body water (TBW), it remains uncertain whether bioimpedance spectroscopic (BIS) approaches are more accurate than single frequency regression equations. The main objective of this study was to answer this question by calculating the expected accuracy of a single measurement for different EBI methods. The results of this study showed that all methods produced similarly high correlation and concordance coefficients, indicating good accuracy as a method. Even the limits of agreement produced from the Bland-Altman analysis indicated that the performance of single frequency, Sun's prediction equations, at population level was close to the performance of both BIS methods; however, when comparing the Mean Absolute Percentage Error value between the single frequency prediction equations and the BIS methods, a significant difference was obtained, indicating slightly better accuracy for the BIS methods. Despite the higher accuracy of BIS methods over 50 kHz prediction equations at both population and individual level, the magnitude of the improvement was small. Such slight improvement in accuracy of BIS methods is suggested insufficient to warrant their clinical use where the most accurate predictions of TBW are required, for example, when assessing over-fluidic status on dialysis. To reach expected errors below 4-5%, novel and individualized approaches must be developed to improve the accuracy of bioimpedance-based methods for the advent of innovative personalized health monitoring applications.

Figure 1

Flow chart of sequence of analytical steps.

Figure 2

Correlation of impedance quotients H ²/R (kHz) and estimated body fluids at different frequencies. Total body water in panel (a) and extracellular fluid in panel (b).

Figure 3

Comparison of TBW volume predicted by impedance methods with TBW measured by tritium dilution. Male data plotted with solid circle and female data with hollow circle.

Figure 4

Limits of agreement between predicted TBW volume and TBW volume determined by tritium dilution; data points are shown by circle while mean ± 2SD limits of agreement and fitted regression line to the data are depicted by dash/dot lines, respectively. The equation of the fitted regression equation, SEE, Pearson correlation coefficient, and mean TBW volume (L and %) are also shown. The values for the limits of agreement are indicated below or under the corresponding line.

Figure 5

Relative deviation Bland-Altman plots combined with distribution plot for the prediction of TBW volume obtained from ²H₂O dilution and 50 kHz single frequency bioimpedance regression equations.

Figure 6

Relative deviation Bland-Altman plots combined with distribution plot for the prediction of TBW volume obtained from tritium dilution and BIS prediction equations.