Expanded Hemodialysis Versus High-Volume Online Hemodiafiltration for Uremic Toxin Removal

Overview

People with advanced kidney disease need dialysis to remove waste products from the blood. Some of these waste products, called uremic toxins, are small, while others are medium-sized and more difficult to remove. Poor removal of these toxins may contribute to symptoms and long-term complications in patients on dialysis. Two dialysis techniques are commonly used to improve toxin removal beyond standard hemodialysis: expanded hemodialysis (HDx) using medium cut-off membranes, and high-volume online hemodiafiltration (HV-OL-HDF). Although both techniques are effective, the best way to prescribe expanded hemodialysis-particularly the ideal treatment time-has not been clearly defined. The purpose of this study is to compare how well different treatment times of expanded hemodialysis remove small and medium-sized uremic toxins, and to compare these results with high-volume online hemodiafiltration. Toxin removal will be evaluated using a combined measurement called the Global Removal Score, which summarizes the removal of several important waste substances. This is a single-center, randomized, open-label, crossover study. Adults receiving maintenance hemodialysis will receive three different expanded hemodialysis sessions with different treatment durations (180, 210, and 240 minutes), followed by one session of high-volume online hemodiafiltration. Blood samples will be taken before and after each dialysis session to measure toxin levels. The results of this study may help determine whether expanded hemodialysis with shorter or standard treatment times can achieve toxin removal similar to high-volume hemodiafiltration, which could support more personalized and practical dialysis prescriptions.

Expanded hemodialysis (HDx) using medium cut-off (MCO) membranes has been developed to improve the removal of medium-sized uremic toxins while maintaining effective clearance of small solutes. These medium-sized molecules have been associated with inflammation, cardiovascular disease, and other complications in patients with end-stage kidney disease. High-volume online hemodiafiltration (HV-OL-HDF) is currently considered a reference therapy for enhanced removal of these toxins, but its use may be limited by technical requirements, vascular access constraints, or resource availability. While expanded hemodialysis has shown removal efficiency comparable to high-volume hemodiafiltration in prior studies, the optimal prescription of HDx-particularly the appropriate treatment duration-has not been clearly established. In routine clinical practice, dialysis dose is commonly guided by small-solute clearance (such as urea), which may not fully reflect the removal of medium-sized uremic toxins. A more comprehensive evaluation of toxin removal may help optimize dialysis prescriptions and improve treatment personalization. This study is designed to compare the efficiency of uremic toxin removal across different expanded hemodialysis treatment durations and to contrast these results with high-volume online hemodiafiltration. Removal efficiency will be assessed using the Global Removal Score, a composite measure that integrates the removal rates of several small and medium-sized molecules while accounting for albumin loss. The study is a single-center, randomized, open-label, crossover trial conducted in adult patients receiving maintenance hemodialysis. Each participant will receive three expanded hemodialysis sessions with different treatment durations (180, 210, and 240 minutes), administered in randomized sequences following the long interdialytic interval. After completion of the three expanded hemodialysis sessions, all participants will undergo one session of high-volume online hemodiafiltration with a predefined convective volume target. During each study session, blood samples will be collected immediately before and after dialysis to measure concentrations of selected uremic toxins, including small solutes and medium-sized molecules. These measurements will be used to calculate individual and global removal rates for each dialysis modality and treatment duration. Standard dialysis parameters will be maintained according to institutional practice to ensure patient safety and consistency across sessions. The crossover design allows each participant to serve as their own control, reducing variability related to patient-specific factors. The primary analysis will compare global toxin removal between expanded hemodialysis prescriptions and high-volume online hemodiafiltration, as well as across different HDx treatment durations. The findings of this study may help clarify whether expanded hemodialysis with shorter or standard treatment times can achieve toxin removal comparable to high-volume hemodiafiltration. This information could support more individualized dialysis prescriptions and inform clinical decision-making in settings where high-volume hemodiafiltration is not feasible or routinely available.