['Sub-analyses of three large trials showed that hemodiafiltration (HDF) patients who achieved the highest convection volumes had the lowest mortality risk. The aims of this study were (1) to identify determinants of convection volume and (2) to assess whether differences exist between patients achieving high and low volumes.', 'HDF patients from the CONvective TRAnsport STudy (CONTRAST) with a complete dataset at 6 months (314 out of a total of 358) were included in this post hoc analysis. Determinants of convection volume were identified by regression analysis.', 'Treatment time, blood flow rate, dialysis vintage, serum albumin and hematocrit were independently related. Neither vascular access nor dialyzer characteristics showed any relation with convection volume. Except for some variation in body size, patient characteristics did not differ across tertiles of convection volume.'] Does treatment policy rather than patient characteristics determine convection volume in online post-dilution hemodiafiltration?