Different body fluid volumes measured by single- and multi-frequency bioelectrical impedance analyzers in overweight/obese renal patients.

Introduction: Bioelectrical impedance analysis (BIA) is an affordable, non-invasive and fast alternative method to assess body composition. The purpose of this study was to compare two different tetrapolar BIA devices for estimating body fluid volumes and body cell mass (BCM) in a clinical setting among patients with kidney failure.

Methods: All double measurements were performed by multi-frequency (MF) and single-frequency (SF) BIA analyzers: a Body Composition Monitor (Fresenius Medical Care, Germany) and BIA-101 (Akern, Italy), respectively. All procedures were conducted according to the manufacturers' instructions (dedicated electrodes, measurement sites, positions, etc). Total body water (TBW), extracellular water (ECW), intracellular water (ICW) and BCM were compared. The study included 39 chronic kidney disease patients (stage III-V) with a mean age of 45.8 ± 8 years (21 men and 18 women) who had a wide range of BMI [17-34 kg/m2 (mean 26.6 ±5)].

Results: A comparison of results from patients with BMI <25 vs ≥25 revealed a significant discrepancy in measurements between the two BIA devices. Namely, in the group with BMI <25 (n=16) acceptable correlations were obtained in TBW (r 0.99; p<0.01), ICW (0.92; p<0.01), BCM (0.68; p<0.01), and ECW (0.96 p<0.05), but those with BMI ≥25 (n=23) showed a discrepancy (lower correlations) in TBW (r 0.82; p<0.05), ICW (0.78; p<0.05), BCM (0.52; p<0.05), and ECW (0.76; p<0.01).

Conclusions: Since estimates of TBW, ICW and BCM by the present BIA devices do not differ in patients with BMI <25, they might be interchangeable. This does not hold true for overweight/obese renal patients.