The impact of hydration status on the assessment of lean body mass by body electrical impedance in dialysis patients.

The impact of hydration status on body composition analysis in hemodialysis (HD) and peritoneal dialysis (PD) patients was assessed. Twenty-seven HD patients and 42 PD patients were divided into three groups according to their (postdialytic) hydration status as measured by segmental bioelectrical impedance analysis (BIA): normohydrated, dehydrated, or overhydrated. Fifty-six percent of the PD patients and 74% of the HD patients appeared to be normohydrated. Lean body mass (LBM) was calculated in all subjects from skinfold anthropometric (SA) measurements and from whole body BIA data. LBM-SA and LBM-BIA did not differ in normohydrated patients and correlated well with each other (r = 0.88). In overhydrated subjects BIA overestimated LBM compared to SA; in the dehydrated group BIA tended to underestimate LBM. The correlation between LBM-SA and LBM-BIA was poor in both groups. It can be concluded that hydration status has a major influence on BIA-based LBM measurements. Reliable LBM figures can only be obtained when patients are at their ideal dry weight.