Use of bioelectrical impedance analysis to measure total body water in patients with cystic fibrosis.

The purpose of this study was to measure whole-body bioelectrical variables and to validate the technique of bioelectrical impedance analysis (BIA) as a measure of total body water (TBW) in patients with cystic fibrosis (CF). In 20 normally nourished males with CF, aged 7 to 39 years, bioelectrical impedance measurements were compared with TBW measured by isotopic distribution of H2(18)O. The relationship between the two measurements was found to be highly significant (r = 0.96; p < 0.0001). The major genotype mutation delta F508 was found to have no effect on BIA. Comparison of the CF patients with 21 normal controls matched for age and TBW volumes as measured by H2(18)O volume of distribution showed no difference in electrical parameters. However, the slope of the regression lines (H2(18)O, H2/R) was significantly steeper for the CF subjects (p < 0.03) than for controls. These data show that BIA can be used to measure TBW in patients with CF. However, the predictive equations developed in healthy control subjects should not be used; rather, separate predictive equations for patients with CF will need to be developed.