Abstract: Objectives  This study aimed to investigate the effects of online hemodiafiltration (OL-HDF) dilution methods and substitution fluid volume on dialysis quality in maintenance hemodialysis (MHD) patients.  Method  A total of 81 patients with MHD were divided into three groups: group A (predilution, substitution volume 18L), group B (predilution, substitution volume 36L) and group C (postdilution, substitution volume 18L). The solute clearance rates, cardiovascular benefits, quality of life, and incidence of adverse reactions were compared among the three groups after 12 months of treatment.  Results  After treatment, the levels of serum phosphorus (P), serum creatinine (Scr) and cystatin C(Cyst-C) in group B were higher than those in groups A and C (B vs. A：t=-2.056、-4.224、-0.349，P=0.045、＜0.001、0.029；B vs. C：t=3.070、4.633、4.110，P=0.003、＜0.001、＜0.001), while the urea clearance index (Kt/V) was lower than that of groups A and C (Kt/V >1.2; B vs. C:t=-4.932，P＜0.001; A vs.  B:t=2.213，P=0.031). Group B had significantly lower levels of β2-microglobulin (β2-MG), intact parathyroid hormone (iPTH), and C-reactive protein (CRP) than Group A (t=0.775, -2.205, 3.145; P=0.042, 0.032, 0.003). Group B had significantly lower carotid intima-media thickness and left ventricular mass index levels than Groups A and C (A vs. B: t=3.116, 2.934; P=0.003, 0.005; B vs. C: t=-2.126, -0.243; P=0.038, 0.009). Its left ventricular ejection fraction (B vs. C: t=3.429, P=0.001; B vs. A: t=-5.107, P＜0.001) and quality of life scores (B vs. A: t=-3.494, P=0.001; B vs. C: t=2.988, P=0.004) were significantly higher than Groups A and C. The incidence of adverse reactions in Group B was significantly lower than in Group A (t=0.448, P=0.006) and Group C (t=0.687, P=0.009). Conclusion The predilution mode with double the substitution fluid volume (36L) can, while ensuring dialysis adequacy, reduce hospitalization and cardiovascular mortality rates, improve quality of life, and demonstrate a higher safety profile.

Key words: Online hemodiafiltration, Predilution, Postdilution, Substitution fluid volumes