Purpose: The dialysis dose is usually assessed by Kt/V urea; however, it is possible that middle molecule (MM) removal could play a role in optimal treatment. Vitamin B12 is a classical MM marker and Kd-B12 is used to compute a MM-based dialysis index, requiring a weekly total clearance (Kd-B12 + renal creatinine clearance (CrCl) > or =30 L, corresponding to IDB12> or =1 (Babb et al, Kidney Int, 1975). Recently, it was demonstrated that by increasing the total Kd-B12 per session (TCV) from 10 to 16 and to 26 L, the relative risk (RR) of death was reduced from 1 to 0.79 and to 0.62, respectively (Leypoldt et al, Am J Kidney Dis 1999). This implies that a minimum TCV of 16 L, but preferably of 26 L per session, should be delivered, for anuric HD patients on a 3x/wk schedule. To extend these results to the whole hemodialysis (HD) population, we suggest transforming TCV into the corresponding IDB12 values: i.e. a TCV=10 L on 3x/wk corresponds to IDB12=1, a TCV=16 and 26 L corresponds to IDB12=1.6 and 2.6, respectively.
Methods: This study aimed to assess Kd-B12 and IDB12 for all stable patients in our unit. There were 62 patients (33 males, 29 females): five patients were being dialyzed once per week (1x), nine patients twice (2x), 46 patients three (3x) and two patients four times (4x) per week (wk); the session length was 232+/-18 min. Most dialyzers had a large surface area (mean 1.9+/-0.3 m2), with KoA-B12=211+/-92 mL/min. Eleven patients, 3x/wk, were on hemodiafiltration (HDF): the reinfusion rate was 33+/-3 mL/min in five patients (sHDF) and 76+/-12 mL/min in six patients (HDF on-line (OL). Kd-B12 was computed as a function of KoA-B12, effective plasma flow, Qd and ultrafiltrate (UF). IDB12 was computed from Kd-B12, ses-sion length and schedule, CrCl and body surface area.
Results: The main results are given below: [table: see text] On average, Kd-B12 was 105 +/- 13 mL/min on HD and 152+/-34 mL/min on HDF. A significant difference was found only for HDF-OL and was essentially due to the higher UF. Of note, the presence of renal function allowed good IDB12 values for 1x/wk and 2x/wk patients, even better than for the standard 3x/wk patients.
Conclusions: We have demonstrated that most available dialyzers provide high Kd-B12 values (but HDF-OL performs significantly better) and that IDB12, by quantifying the impact of UF, session length, schedule and renal function, allows the assessment of dialysis adequacy beyond Kt/V urea, for all HD or HDF patients, on a routine basis and at no added cost.