Bioimpedance analysis in patients with chronic kidney disease

In recent years the use of bioimpedance analysis (BIA) for assessment of fluid status as well as body composition as a mean to assess nutritional status in CKD has increased. The interest in the method is due to the associations between fluid overload and cardiovascular disease, and between fluid overload and malnutrition, both of which contribute to an increased risk of morbidity and mortality (Hur et al., 2013; Onofriescu et al., 2014). Moreover, BIA devices are suitable for clinical use, since they are portable, easy to use and, with a median to low price. However, the results can be difficult to interpret and integrate into routine clinical care, and although impedance measurements can contribute to an increased understanding of the patient's fluid balance, the results should be used with caution and in combination with other physiological parameters and clinical assessments (de Ruiter et al., 2020; Scotland et al., 2018). The aim of this editorial is to contribute to increased awareness of the benefits and limitations of using bioimpedance in patients with CKD with or without dialysis, and contribute to improving the measurement quality, facilitating interpretations, and highlighting possible sources of error.

BIA can be defined as the resistance measured by a weak alternating current when conducted through biological tissue. The conductivity differs between different tissues, which makes it possible to estimate body composition and fluid balance. BIA equipment measures impedance, which includes the reactance (capacitive impedance in cell membranes and other structures) and resistance (resistance due to extracellular [ECW] and intracellular water [ICW]). These variables can be measured with good precision and reproducibility between different devices (Kyle et al., 2004).

However, it is of fundamental importance to understand the limitations of BIA technology to avoid unrealistic expectations of measurement accuracy and precision (Ward, 2019). Deriving body composition information from impedance data includes estimated and assumed parameters and the use of population-averaged factors, such as body shape. Although it is plausible that prediction equations could be improved by including more individual-level information (e.g., the use of plasma sodium to improve estimations of tissue resistivity (Mitsides et al., 2020; Schneditz et al., 2023) this would have huge implications for the ease of use and applicability of the technology.

Variations in agreement between different impedance techniques and devices as well as with reference methods for measuring body composition can largely be attributed to the choice of method and device-specific software (Kyle, 2004; Kyle et al., 2004; Sheean et al., 2020). Also, each manufacturer of BIA equipment designs its own software for analysis and description of measurement results; this makes direct comparisons between different devices uncertain, and it would be difficult to give universal advice on how to use bioimpedance in day-to-day clinical management of patients with CKD. Therefore, although many of the guiding principles in this paper can be translatable to various devices, we will hence forward primarily be referring to the Body Composition Monitor (BCM®; Bad Homburg) a device which has been validated in patients with CKD (Davies et al., 2017; Marcelli et al., 2015; Wabel et al., 2009).

As kidney failure progresses from early stages through to end-stage kidney failure, body composition is increasingly affected, including fluid retention and loss of muscle mass. Unless bioimpedance results deviate significantly from reference values, a single measurement provides limited information, but repeated measurements over time provide the most valuable information. If the measurement conditions deviate from the normal, it is especially important to have a structured and uniform methodology. Carefully conducted measurements, performed over time, probably reflect actual changes in body composition (Kyle, 2004; Kyle et al., 2004; van der Sande et al., 2020). When conducting impedance measurements, pay attention to the recommendations in Table 1.

An impedance measurement generates a multitude of data. Impedance devices of various manufactures may report fluid balance and body composition output in different ways. For assessment of fluid status and nutritional status with bioimpedance, the variables in Tables 2 and 3 are commonly used:

Epidemiological studies clearly demonstrate the association between BIS measurements and important outcomes for HD patients at the population level. However, results from clinical trials suggest that the incorporation of BIS into routine clinical management is challenging. Unless results from BIS measurements deviate significantly from reference values, a single measurement provides limited information. Carefully conducted measurements, however, performed over time, probably reflect actual changes in fluid status and body composition. If the measurement conditions deviate from the normal, it is especially important to have a structured and uniform methodology for follow up and, if possible, perform repeated measurements or use a reference method, for example, dual-energy X-ray absorptiometry. We believe that by better understanding of the fundamental differences between bioimpedance devices, principles of measurement and incorporation of the results with clinical assessment as part of decision support tools may better support use of BIS at the individual level.

The members of the SWEBIS network agree to the submission of the manuscript to the Journal of Renal Care. All authors fulfil the ICMJE requirements for authorship and contributed to the manuscript. Sintra Eyre and Jenny Stenberg were principal project leaders and responsible for the main drafting of the manuscript, with special contributions, design and coordination made by Ola Wallengren and David Keane. All the other authors (Carla M. Avesani, Ingvar Bosaeus, Naomi Clyne, Olof Heimbürger, Ainhoa Indurain, Ann-Cathrine Johansson, Bengt Lindholm, Fernando Seoane, Mia Trondsen) made critical revisions and participated with important intellectual content, read, and approved the final manuscript.

Jenny Stenberg: Honoraria for lectures from AstraZeneca, Baxter Healthcare and Fresenius Medical Care. Ola Wallengren: Personal speakers fee from Fresenius Kabi AB for educational lectures. Carla M. Avesani: C. M. A. declares no conflict of interest with the current paper. C. M. A. received payment for lectures from Astra Zeneca, Fresenius Medical Care and Baxter healthcare and participation in Advisory board for Astra Zeneca. Olof Heimbürger: Honoraria for lectures from Baxter Healthcare, Fresenius Medical Care, Astra Zeneca, ewimed and Vifor. Ann-Cathrine Johansson: Personal speakers fee from Fresenius AB. Bengt Lindholm: Affiliated with Baxter Healthcare: Previous employment; owns stock; Baxter Novum is supported by grant from Baxter Healthcare to Karolinska Institutet. The remaining authors declare no conflict of interest.

This guideline for the clinical use of bioimpedance in patients with CKD was developed by the Swedish Bioimpedance Network (SWEBIS), which is an interprofessional network of people interested in the clinical application of bioimpedance in patients with chronic kidney disease (CKD). The network, which was initiated in 2014, consists of dieticians (SE, CA, OW), physiotherapists (MT), nurses (JS), physicians (ACJ, IB, NC, OH, AI, BL), and engineers/physicist (DK, FS).