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

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 (height2/R500 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 (r2adj of 0.81 (P < 0.0001) and a root mean square error (RMSE) of 3.61 (9%). Cross-validation of the predictive algorithm in the remaining 15 subjects gave an r2adj of 0.87 (P < 0.0001) and an RMSE of 3.01 (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.