Bioimpedance Analysis for the Assessment of Body Composition and Relation with Muscle Strength in Patients with CKD Stage G3 to G5 and Healthy Controls

Background: Bioimpedance analysis (BIA) is an increasingly used method to assess body composition (BC) and the prevalence of sarcopenia in patients with chronic kidney disease (CKD). BIA measurement can be performed at a whole-body level by the Body Composition Monitor (BCM). The InBody S10 Biody Water Analyzer (BWA) enables additional modelling of body segments, extremities and trunk, whereas BCM allows for assessment of overhydration as a separate compartment. This study compares BCM and BWA measurements with respect to assessment of fat free mass (FFM) and its association with handgrip strength (HGS) in patients with CKD stage G3 to G5 and in healthy controls. Methods: This is a prospective observational study. 50 patients with CKD (23 stage G3 and 27 stage G4-5) and 30 control subjects were included. BC was assessed with the BCM and BWA. HGS was measured to assess muscle strength. BCM and BWA measurements were analyzed with Bland-Altman plots. The relation between BC and HGS in relation to renal function was assessed with multivariable analysis. Results: FFM of the BCM was 1.4 kg higher than the BWA (95%-CI=0.016 to 2.78, p=0.047, limits of agreement -7.3 to 10.1) for the CKD group and 1.8kg lower for the controls (95%-CI=-3.25 to -0.40, p=0.014, limits of agreement -8.4 to 4.8). Body cell mass (BCMa) of the BCM was 8.1kg lower than the BWA (p=<0.001) for the CKD group and 10.6kg lower for the controls (p=<0.001). HGS was significantly correlated with FFM-BCM (for CKD: B=0.6, 95%-CI=0.4 to 0.9, β=0.59, p=<0.001 and for controls: B=0.7, 95%-CI=0.5 to 0.8, β=0.87, p=<0.001) and with FFM-BWA (for CKD: B=0.8, 95%-CI=0.5 to 1.0, β=0.65, p=<0.001 and for controls: B=0.6, 95%-CI=0.4 to 0.8, β=0.86, p=<0.001). Conclusion: FFM estimates was significantly different between BCM and BWA for both the CKD group and the healthy controls. The large difference in BCMa might be attributed to differences in expression of BC compartments between the BCM and BWA. Both FFM and BCMa showed high individual variability. FFM assessed by both methods significantly correlated to HGS. Future studies will have to define whether device specific cut-off reference values of BIA estimates are needed to enhance its applicability in clinical care for CKD patients.