Beyond Diffusion: Clinical Perspectives on Online Hemodiafiltration and Medium Cut-Off Dialyzers

Online hemodiafiltration (OL-HDF) and medium cut-off (MCO) dialyzers augment diffusion-based hemodialysis (HD) with convective clearance to enhance removal of middle molecules. In large-scale randomized trials, OL-HDF appears to reduce all-cause, cardiovascular, and infection-related mortality compared with high-flux HD, particularly when convection volumes exceed 23 L per session. Data suggest a graded effect; higher achieved convection volumes are associated with greater benefit, and advantages have been observed across the analyzed subgroups. Evidence also indicates better preservation of patient-reported quality of life compared with high-flux HD. Large-scale observational registry data, while subject to inherent limitations, support beneficial outcomes and generalizability to routine clinical practice. MCO membranes enhance middle-molecule clearance on conventional hemodialysis machines via enlarged pore size and internal-filtration back-filtration. However, the long-term clinical data remain limited, and the convective component is not externally measured or prescribed. This perspective distils mechanistic and clinical insights on both OL-HDF and MCO-HD and evaluates the published evidence, including solute clearance studies, mortality outcomes, and patient-reported quality-of-life data. We outline actionable prescription strategies and opportunities for individualized treatment optimization. Our goal is to provide clinicians with a concise roadmap to personalize and integrate convection-enhancing therapies in everyday practice.