Estimate of body water compartments and of body composition in maintenance hemodialysis patients: comparison of single and multifrequency bioimpedance analysis.
OBJECTIVE
The goal of this study was to compare the adequacy of single and multifrequency bioimpedance analysis (BIA) to evaluate body water compartments, body composition, and nutritional status in maintenance hemodialysis patients.


DESIGN
Cross-sectional study.


SETTING
University-based hemodialysis unit.


PATIENTS
Nineteen patients (12 male, 7 female), ages 28 to 82 years (mean, 58.9), treated with maintenance hemodialysis (MHD) for 0.5 to 15 years (mean, 7.3).


INTERVENTION
This was a noninterventional study. Patients gave their informed consent to the diagnostic procedures performed.


MAIN OUTCOME MEASURES
Total body water (TBW), extracellular water (ECW), fat-free mass (FFM), and body cell mass (BCM) volumes were estimated with single-frequency (sf BIA) and multifrequency (mf BIA) plethysmographs before and after a midweek dialytic session. Predialysis TBW also was estimated from anthropometric data (e TBW). Serum albumin, prealbumin and myoglobin, and creatinine index were determined as indicators of nutritional status and muscle mass.


RESULTS
Sf BIA and mf BIA gave very similar results for TBW volumes. A high linear correlation was also found between e TBW values and both sf TBW and mf TBW; however, a statistically significant difference was found between e TBW and sf and mf TBW. Sf BIA and mf BIA gave quite different results for ECW, particularly when measured predialysis. The results obtained for FFM indicate a poor agreement between sf and mf BIA. The agreement was better when FFM was measured postdialysis. The values of BCM, either measured predialysis or postdialysis, indicate a significant difference between sf and mf BIA. FFM and BCM estimated with mf BIA had a closer correlation with creatinine index than sf BIA. mf BCM had also a higher correlation with serum myoglobin, which is produced by muscle cells.


CONCLUSIONS
TBW can be estimated with enough confidence from either sf or mf BIA at any time. On the contrary, the results of ECW are significantly different with sf and mf BIA when measured predialysis. Thus, it seems more convenient to perform BIA after dialysis, in particular when assessing the "ideal" body weight. The measurements of FFM and BCM, obtained with either sf or mf BIA, are correlated with different indicators of nutritional status. In particular, mf BCM seems more appropriate than sf BCM for estimating muscle mass.