Accuracy of an eight-point tactile-electrode impedance method in the assessment of total body water

Abstract

Objective: To establish the accuracy of an eight-polar tactile-electrode impedance method in the assessment of total body water (TBW). Design: Transversal study. Setting: University department. Subjects: Fifty healthy subjects (25 men and 25 women) with a mean (s.d.) age of 40 (12) y. Methods: TBW measured by deuterium oxide dilution; resistance (R) of arms, trunk and legs measured at frequencies of 5, 50, 250 and 500 kHz with an eight-polar tactile-electrode impedance-meter (InBody 3.0, Biospace, Seoul, Korea). Results: An algorithm for the prediction of TBW from the whole-body resistance index at 500 kHz (height 2 =R 500 where R is the sum of the segmental resistances of arms, trunk and legs) was developed in a randomly chosen subsample of 35 subjects. This algorithm had an adjusted coefficient of determination (r 2 adj ) of 0.81 (P < 0.0001) and a root mean square error (RMSE) of 3.6 l (9%). Cross-validation of the predictive algorithm in the remaining 15 subjects gave an r 2 adj of 0.87 (P < 0.0001) and an RMSE of 3.0 l (8%). The precision of eight-polar BIA, determined by measuring R three times a day for five consecutive days in a fasting subject, was 2.8% for all segments and frequencies. Conclusion: Eight-polar BIA is a precise method that offers accurate estimates of TBW in healthy subjects. This promising method should undergo further studies of precision and its accuracy in assessing extracellular water and appendicular body composition should be determined. Sponsorship: Modena and Reggio Emilia University.

Body water distribution in severe obesity and its assessment from eight-polar bioelectrical impedance analysis

“…The regression lines had similar slopes and intercepts (data not shown), confirming the manufacturer's indication that this apparent violation of the conduction pathways is expected to have a minimal effect on the assessment of body composition. The within-day precision of InBody 3.0 in three obese subjects was p2.0 O, a value similar to that observed in nonobese subjects (Bedogni et al, 2002;Malavolti et al, 2003).…”

“…As in our previous study (Bedogni et al, 2002), we developed an equation for predicting TBW from RI 500 (panel a1 of Figure 2). RI 500 explained 82% of TBW variance (Po0.0001) and the RMSE% was 5%.…”

“…Sample size was determined by considering that a sample of 25 subjects has a power of 0.99 to detect a slope of 1.00 at an alpha level of 0.05 when the standard deviation of TBW is 4 l and that of RI 500 is 3 O (Bedogni et al, 2002). Aiming at comparing nonobese, class I-II obese, and class III obese women, we enrolled 75 (25 * 3) subjects.…”

“…Eight-polar BIA is a recently introduced technique with three interesting characteristics: (1) the use of very practical tactile electrodes for measuring segmental resistances at multiple frequencies, (2) the absence of need to standardize subject's posture before analysis and, (3) the rapidity of measurements. We have shown that eight-polar BIA offers accurate estimates of TBW and appendicular body composition in adult and elderly subjects (Bedogni et al, 2002;Malavolti et al, 2003). However, the accuracy of eightpolar BIA in detecting TBW and ECW in conditions of altered body water distribution is at present unknown.…”

“…We avoided measuring segmental lengths and calculating segmental RIs because the above approach is at least as accurate as the segmental one and less time consuming (Bedogni et al, 2002;Malavolti et al, 2003). No caution was taken to standardize the subject's posture before BIA, as suggested by the manufacturer.…”