Development of anthropometry-based equations for the estimation of the total body water in Koreans

For developing race-specific anthropometry-based total body water (TBW) equations, we measured TBW using bioelectrical impedance analysis (TBWBIA) in 2,943 healthy Korean adults. Among them, 2,223 were used as a reference group. Two equations (TBWK1 and TBWK2) were developed based on age, sex, height, and body weight. The adjusted R2 was 0.908 for TBWK1 and 0.910 for TBWK2. The remaining 720 subjects were used for the validation of our results. Watson (TBWw) and HumeWeyers (TBWH) formulas were also used. In men,TBWBIA showed the highest correlation with TBWH, followed by TBWK1, TBWK2 and TBWw. TBWK1 and TBWK2 showed the lower root mean square errors (RMSE) and mean prediction errors (ME) than TBWw and TBWH. On the Bland-Altman plot, the correlations between the differences and means were smaller for TBWK2 than for TBWK1. On the contrary, TBWBIA showed the highest correlation with TBWw, followed by TBWK2, TBWK1, and TBWH in females. RMSE was smallest in TBWw, followed by TBWK2, TBWK1 and TBWH. ME was closest to zero for TBWK2, followed by TBWK1, TBWw and TBWH. The correlation coefficients between the means and differences were highest in TBWw, and lowest in TBWK2. In conclusion, TBWK2 provides better accuracy with a smaller bias than the TBWw or TBWH in males. TBWK2 shows a similar accuracy, but with a smaller bias than TBWw in females.