Single-Pool Kt/V for β2-Microglobulin Highlights Differences Between Hemodiafiltration and Expanded Hemodialysis Therapies

Background: Elevated levels of Beta-2-microglobulin (β2m) in patients undergoing hemodialysis have been associated with increased mortality. Convective therapies such as hemodiafiltration (HDF) and expanded hemodialysis (HDx) enhance clearance of middle weight molecules (MWM), with β2m serving as a representative marker. This study aimed to evaluated and compare the efficacy of HDF and HDx in β2m removal, using a modified single-pool Kt/V (spKt/V b2m). Methods: From July 2024 to April 2025, monthly pre and post dialysis β2m and BUN levels were collected in our center. We analyzed 264 sessions from 36 patients (21 on HDF, and 15 on HDx). The spKt/V b2m was calculated using the Casino et al formula: spKt/V b2m = 6.12DW/W [1−ln (Ct / C0) / ln (1 + 6.12DW/W)] where DW/W is the net ultrafiltration volume relative to post-dialysis weight, C0 and Ct are pre and post dialysis β2m concentrations. This derives from Leypoldt’s clearance model: K b2m = Qf [1−ln (Ct / C0) / ln (1 + Qf * Td / V b2m)] Qf: net fluid removal rate (mL/min); Td session duration (min); V β2m: distribution volume for β2m, assumed to be one-third of urea distribution volume (Vurea = 49% of body weight). The equilibrated Kt/V (eKt/V b2m) was calculated as: eKt/V b2m = spKt/V b2m * Td / (Td + 110) Results: All dialysis sessions lasted 240 minutes. The mean Qb was 364 ±18 mL/min, Qd 482 ± 51 ml/min, and net weight loss 2.1 ± 0.8 kg. In HDF mean convective volume was 27.2 ± 3.2 L/session. HDF demonstrated significantly higher β2m clearance than HDx: K b2m 125.4 ± 20.6 vs 115.0 ± 30.3 ml/min (p =0.001), spKt/V b2m 3.2 ± 0.3 vs 2.7 ± 0.2 (p <0.001), and eKt/V b2m 2.2 ± 0.2 vs 1.8 ± 0.1 (p <0.001) (Fig. 1). Conclusion: HDF demonstrated superior β2m removal compared to HDx, supported by higher of K b2m, spKt/V b2m and eKt/V b2m. These findings reinforce the advantage of convective therapies for MWM clearance in chronic hemodialysis patients.