Exploring Biomarkers for Excess Extracellular Fluid in the Context of Physical Function in Chronic Kidney Disease Patients

<b>Background/Objectives</b>: Fluid overload is an important risk factor for protein-energy wasting, which could lead to poor outcomes, such as higher morbidity and mortality, in patients with chronic kidney disease (CKD). This study aimed to validate the possible myokine as a biomarker of volume status in patients with non-dialysis CKD. <b>Methods</b>: In total, 151 patients with CKD were enrolled from a single medical center. Demographic data were collected via medical record review. Bioimpedance analysis was performed to measure body composition, and physical performance was assessed by measuring hand grip strength. <b>Results</b>: The physical performance of hand grip strength (21.9 ± 8.7 vs. 19.0 ± 10.1 kg, <i>p</i> = 0.233) and walking speed (1.05 ± 0.29 vs. 0.86 ± 0.52 m/s, <i>p</i> = 0.192) was higher in the low extracellular water/total body water (ECW/TBW) ratio group. Although higher, the median value of the brain-derived neurotrophic factor (BDNF) was not significant in the low ECW/TBW ratio group. Despite that, it had significant negative correlations with the ECW/TBW ratio in Pearson's correlation analyses (r = -0.329, <i>p</i> < 0.001; r = -0.287, <i>p</i> < 0.001; and r = -0.238, <i>p</i> = 0.003). Linear regression analysis showed that the BDNF level had a significant negative relationship with the ECW/TBW ratio and significant associations even after multivariate analysis. <b>Conclusions</b>: Among myokines, BDNF had a significant negative relationship with the ECW/TBW ratio, suggesting that BDNF could be a possible biomarker for volume status in patients with non-dialysis CKD.