Comparison of anthropometric equations for estimation of total body water in peritoneal dialysis patients

Background. Several formulae exist for estimating total body water (TBW). We aimed to assess their validity in peritoneal dialysis patients by comparison with TBW estimated by deuterium oxide dilution (TBWD). Methods. We compared the equations of Chertow (TBWCher), Chumlea (TBWChum), Hume and Weyers (TBWHW), Johansson (TBWJ), Lee (TBWL), Watson (TBWW) and TBW as 58% of body weight (TBW0.58Wt) with TBWD in 31 peritoneal dialysis (PD) patients and 32 controls. Estimates were compared with TBWD using Bland and Altman comparison. Extracellular water (ECW) was also estimated by sodium bromide dilution. Results. In PD patients, mean TBWD was 35.04 (SD 7.84) 1. Estimates were greater for TBWCher, TBWChum, TBWHW, TBWJ and TBW0.58Wt. Mean TBWL and TBWW did not differ from TBWD. Ninety-five percent limits of agreement (LOA) compared with TBWD (as a percentage of the mean) were similar for all of the different equations in PD patients (between +/-15.4 and +/-17.3%) except TBW0.58Wt, which was far greater (+/-26.4%). In controls, mean TBWD was 37.03 (SD 6.63) 1. Estimates were greater for TBWCher, TBWChum, TBWHW, TBWJ and TBW0.58Wt. Mean TBWL and TBWW did not differ from TBWD. Ninety-five percent LOA compared with TBWD (as a percentage of the mean) were similar for all equations in the controls, and closer than in PD patients (between +/-9.1 and +/-11.5%) except TBW0.58Wt, which was again far greater than the other equations (+/-28.1%). TBWHW - TBWD correlated with mean TBW (r=-0.412, P<0.05 in PD and r=-0.383, P<0.05 in controls). TBWW - TBWD (r=-0.539, P<0.005) correlated with mean TBW in PD. TBW0.58Wt - TBWD correlated with body mass index (BMI) (r=0.624, P<0.0001 in PD and r=0.829, P<0.0001 in controls) and ECW/TBW (r=0.406, P<0.05 in PD and r=0.411, P<0.02 in controls). Conclusions. Predictive equations were less accurate in PD than controls. TBW0.58Wt was most inaccurate, with systematic overestimation of TBW with increasing BMI and ECW/TBW. There were no differences in LOA with TBWD for the other equations within each group.