CORRELATION BETWEEN CHANGES IN THE BODY FLUID VOLUME CALCULATED BY THE URIC ACID KINETIC MODEL AND CHANGES IN THE BODY WEIGHT

Abstract Background and Aims Uric acid (UA) is a solute unable to cross the cell membranes in general tissues by any of simple diffusion, facilitated diffusion or active transport. These facts imply that UA distribution volume (UDiV) equals to the extracellular fluid volume (ECFV). We have developed a method for calculating UDiV from serum uric acid levels before and after hemodialysis based on a uric acid kinetic model (Shinzato T, Int J Artif Organs 2020). Urea is evenly distributed throughout the body fluids. Therefore, the total body fluid volume (TBFV) can be calculated by using the same method as the calculation of UDiV for the serum urea level. The remaining body fluid volume, which is TBFV minus UDiV, is considered to reflect the intracellular fluid volume (ICFV). In this study, we clarified the relationship between the amount of change over time in UDiV and ICFV calculated by the uric acid kinetic model and the amount of change over time in the actual body weight of hemodialysis patients. Method Subjects were 1,101 patients with chronic maintenance hemodialysis. UDiV and ICFV before and after dialysis were calculated for two time points, December 2019 and June 2020. Results The amount of change in UDiV per body during the dialysis session showed a very good correlation with the amount of body weight change during the same dialysis (UDiV change = 0.950 x body weight change - 0.158, R-square 0.90, p < 0.0001). The amount of change in ICFV during the 6 months from December 2019 to June 2020 showed a good correlation with the amount of change in post-dialysis body weight during the same period (ICFV change = 0.270 x post-dialysis body weight change + 0. 240, R-square 0.21, p <0.0001). Conclusion These results suggest that the body fluid volume calculated by the uric acid kinetic model has high accuracy.