ABSTRACT Introduction Hyperphosphatemia is frequent in hemodialysis (HD) patients and associates with cardiovascular mortality. Parameters of online hemodiafiltration (OL‐HDF) prescription influencing phosphate removal are poorly understood in real‐world clinical settings. Methods We conducted a prospective observational study including chronic HD patients dialyzed at a single UK university hospital between December 2021 and July 2023. Phosphate removal was quantified from spent dialysate during a midweek session. Results Dialysate phosphate was measured during 161 dialysis sessions in 128 unique patients (19 on HD and 109 on OL‐HDF), with mean age 63.3 ± 16.2 years and 77 (60.1%) men. Mean intra‐dialytic phosphate removal was 25.6 ± 14.3 mmol per session. In multivariate analysis, pre‐HD serum phosphate concentration, session time, and urea distribution volume ( V ) were positively associated with intradialytic phosphate removal. A significant interaction between session time and pre‐HD serum phosphate concentration indicated that longer sessions provided greater benefit to patients with higher baseline phosphate levels. Conversely, dialysis modality (OL‐HDF vs. HD) and substitution volume were not significantly associated with phosphate removal. Conclusions OL‐HDF and substitution flow do not demonstrate a measurable beneficial impact on phosphate removal in a real‐world setting. Session time, pre‐HD serum phosphate concentration, and urea distribution volume ( V ) are the most relevant determinants of phosphate clearance in real‐world clinical practice. Session duration emerges as the most effective modifiable factor for controlling phosphate burden in dialysis patients, particularly for those with higher pre‐HD phosphate levels.
Jaques et al. (Mon,) studied this question.
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