Evaluation of different bioimpedance methods for assessing body composition in Asian non-dialysis chronic kidney disease patients

Background: Chronic kidney disease (CKD) is associated with fluid retention, which increases total body water (TBW) and leads to changes in intracellular water (ICW) and extracellular water (ECW). This complicates accurate assessments of body composition. Analysis of bioelectrical impedance may improve the accuracy of evaluation in CKD patients and multiple machines and technologies are available. We compared body composition by bioimpedance spectroscopy (BIS) against multi-frequency bioimpedance analysis (BIA) in a multi-ethnic Asian population of stable, non-dialysis CKD patients. Methods: We recruited 98 stable CKD patients comprising 54.1% men and 70.4% Chinese, 9.2% Malay, 13.3% Indian, and 8.2% other ethnicities. Stability was defined as no variation in serum creatinine > 20% over three months. Patients underwent BIS analyses using a Fresenius body composition monitor, while BIA analyses employed a Bodystat Quadscan 4000. Results: Mean TBW values by BIS and BIA were 33.6 +/- 7.2 L and 38.3 +/- 7.4 L; mean ECW values were 15.8 +/- 3.2 L and 16.9 +/- 2.7 L; and mean ICW values were 17.9 +/- 4.3 L and 21.0 +/- 4.9 L, respectively. Mean differences for TBW were 4.6 +/- 1.9 L (P < 0.001), for ECW they were 1.2 +/- 0.5 L (P < 0.001), and for ICW they were 3.2 +/- 1.8 L (P < 0.001). BIA and BIS measurements were highly correlated: TBW r = 0.970, ECW r = 0.994, and ICW r = 0.926. Compared with BIA, BIS assessments of fluid overload appeared to be more associated with biochemical and clinical indicators. Conclusion: Although both BIA and BIS can be used for body water assessment, clinicians should be aware of biases that exist between bioimpedance techniques. The values of body water assessments in our study were higher in BIA than in BIS. Ethnicity, sex, body mass index, and estimated glomerular filtration rate were associated with these biases.