Weekly Trends in Phosphate Levels During Hemodiafiltration

Background: Phosphate (P) levels control in patients on dialysis remains a challenge. Hemodiafiltration (HDF) appears to improve P levels, though the literature is limited regarding the evaluation of hyperphosphatemia throughout the week. We hypothesized that P levels would improve during a HDF week, with a reduction in prevalence toward the last sessions. Methods: This cross-sectional, multicenter study aimed to evaluate P levels before dialysis, after 1 hour, and at the end of the procedure in patients on maintenance HDF. Data from all consecutive HDF sessions over one week were included. We have compared P levels according to dialysis shift, frequency (3 vs. 4-6 times per week), and duration. Hyperphosphatemia was defined as pre HDF P levels > 5.5 mg/dL. Results: A total of 79 patients (60.8% male, 44% on conventional, 49.4% on short-daily and 6.3% on long nocturnal HDF) were included in the study. P levels measured before HDF, after 1 hour, and at the end of the procedure did not differ significantly across dialysis shifts, frequency, or session duration (p > 0.05 for all comparisons). A significant reduction in P levels was observed, with decreases of up to 2.5 mg/dL after 1 hour and 2.8 mg/dL at the end of the procedure across all sessions throughout the week. Pre-dialysis P levels decreased from the first to the last session of the week in patients undergoing 3, 5, and 6 sessions of HDF/week. Among the first three HDF sessions, 27.6% of patients exhibited persistent hyperphosphatemia. This group had significantly higher P levels (p<0.001), urea (p=0.014), and parathyroid hormone (PTH) levels (p=0.034) before the first HDF session of the week compared to patients without hyperphosphatemia, who represented 51.3% of the cases. Additionally, 14.5% of patients showed improvement in hyperphosphatemia, which occurred mostly in the second session (72.7%). Conclusion: Hyperphosphatemia remains a challenging issue for patients undergoing HDF. The characteristics of the patients, as well as the timing of P level assessments throughout the week, significantly influence the prevalence of hyperphosphatemia. These findings highlight the need for a standardized approach in assessing hyperphosphatemia in dialysis patients to facilitate comparisons across populations and studies.