Single-frequency and multi-frequency bioimpedance analysis: What is the difference?

Aim Bioelectrical impedance analysis is a promising method in determining the body compartments in hemodialysis patients. In this study, we aimed to investigate the agreement between two widely used methods: the single-frequency and multi-frequency bioelectrical impedance analyses. Methods Maintenance hemodialysis patients were enrolled in the study. Single-frequency and multi-frequency bioelectrical impedance analyses were performed consecutively before hemodialysis. A second bioelectrical impedance analysis was performed right after the hemodialysis session. A third bioelectrical impedance analysis was performed one hour after hemodialysis. We used weight change as a measure of fluid removal during hemodialysis session. Results Bioelectrical impedance analysis estimates from both devices had significant differences. Best agreement was observed between single frequency and multifrequency device at the immediate post hemodialysis extracellular water estimates (mean difference 0,076 L). We found the best agreement between weight change and extracellular water change using single-frequency bioimpedance analysis. Moreover, one hour waiting time did not improve the agreement between weight and extracellular water changes for both devices. Different estimates seem to be caused by different raw impedance data measured by both devices and device specific equations. Conclusion There are significant differences among bioelectrical impedance measurements performed with different bioelectrical impedance analyzers. Using open source software might be an important step forward in the development of standardized measurements.