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 (TBW(D)).

Methods: We compared the equations of Chertow (TBW(Cher)), Chumlea (TBW(Chum)), Hume and Weyers (TBW(HW)), Johansson (TBW(J)), Lee (TBW(L)), Watson (TBW(W)) and TBW as 58% of body weight (TBW(0.58Wt)) with TBW(D) in 31 peritoneal dialysis (PD) patients and 32 controls. Estimates were compared with TBW(D) using Bland and Altman comparison. Extracellular water (ECW) was also estimated by sodium bromide dilution.

Results: In PD patients, mean TBW(D) was 35.04 (SD 7.84) l. Estimates were greater for TBW(Cher), TBW(Chum), TBW(HW), TBW(J) and TBW(0.58Wt). Mean TBW(L) and TBW(W) did not differ from TBW(D). Ninety-five percent limits of agreement (LOA) compared with TBW(D) (as a percentage of the mean) were similar for all of the different equations in PD patients (between +/-15.4 and +/-17.3%) except TBW(0.58Wt), which was far greater (+/-26.4%). In controls, mean TBW(D) was 37.03 (SD 6.63) l. Estimates were greater for TBW(Cher), TBW(Chum), TBW(HW), TBW(J) and TBW(0.58Wt). Mean TBW(L) and TBW(W) did not differ from TBW(D). Ninety-five percent LOA compared with TBW(D) (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 TBW(0.58Wt), which was again far greater than the other equations (+/-28.1%). TBW(HW) - TBW(D) correlated with mean TBW (r=-0.412, P<0.05 in PD and r=-0.383, P<0.05 in controls). TBW(W) - TBW(D) (r=-0.539, P<0.005) correlated with mean TBW in PD. TBW(0.58Wt) - TBW(D) 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. TBW(0.58Wt) was most inaccurate, with systematic overestimation of TBW with increasing BMI and ECW/TBW. There were no differences in LOA with TBW(D) for the other equations within each group.