Objectives: To assess the influence of abnormalities in fluid status and body composition on agreement between multifrequency bioimpedance analysis (MF-BIA), segmental BIA (sigmaBIA), the Watson formula, and tracer dilution techniques.
Design: Cross-sectional.
Setting: Multicenter.
Patients: 40 patients (29 males, 11 females) on peritoneal dialysis (PD).
Main outcome measures: Agreement between the various techniques used to assess total body water (TBW) [MF-BIA, deuterium oxide (D2O), and the Watson formula] and extracellular water (ECW) [MF-BIA, bromide dilution (NaBr), and sigmaBIA], also in relation to the relative magnitude of the body water compartments [ECW (NaBr):body weight (BW) and TBW (D2O):BW] and body composition (DEXA). Second, the relation between body water compartments with echocardiographic parameters.
Results: Wide limits of agreement were observed between tracer dilution techniques and MF-BIA [TBW (D2O - MF-BIA) 2.0 +/- 3.9 L; ECW (NaBr - MF-BIA) -2.8 +/- 3.9 L], which were related to the relative magnitude of the body water compartments: r = 0.70 for ECW and r = 0.40 for TBW. sigmaBIA did not improve the agreement [ECW (NaBr-sigmaBIA): 3.7 +/- 2.9 L]. Also, wide limits of agreement were observed between D2O and the Watson formula (-2.3 +/- 3.3 L). The difference between D2O and Watson was related to hydration state and to percentage of fat mass (r = 0.70 and r = -0.53, p < 0.05). Both ECW and TBW as assessed by BIA and tracer dilution were related to echocardiographic parameters.
Conclusion: Wide limits of agreement were found between MF-BIA and sigmaBIA with dilution methods in PD patients, which were related to hydration state itself. The disagreement between the Watson formula and dilution methods was related to both hydration state and body composition.