Difference between Post and Pre-dilution in Online Haemodiafiltration in the Removal of Median-Molecular-Weight Toxins

This investigation compared the removal rates of two medium-molecular-weight toxins,
2-microglobulin and the even bigger molecule prolactin, using filters with varying surface areas.
2-microglobulin and prolactin are medium-molecular-weight toxins. We consider that the rate of removal of these molecules, using filters with two different surfaces, in post- and pre-dilution haemodiafiltration, it would be helpful to clarify.

We studied, in 12 chronic haemodialyzed patients, the removal of those, with polynephron filter with surface area of 2.5 m2 (Group A) or 2.1 m2 (Group B) with post-dilution haemodiafiltration, and with a filter with surface 2.5 m2 with pre-dilution (Group C).

No differences were found in its percentage change of
2-microglobulin between Groups A and B, while a significant difference was found between Groups A and C (68±6.9 vs 65.2±3.0, p<0.02) and Groups B and C (69.4±3.2 vs 65.2±3.0, p<0.005). The amount of
2-microglobulin removed were differed between Groups A and C (213±76.6 vs 184.2±47.5, p<0.02) and Groups B and C (215.4±48.8 vs 184.2±47.5, p<0.005) (Table 2). For prolactin was found change in percentage only between Groups A and C (54.6±8.89 vs 42.3±8.2, p<0.002) and Groups B and C (58.05±9.1 vs 42.3±8.2, p<0.0002) (Table 3), a fact indicating that less prolactin is removed in pre-dilution on-line HDF (about 12–16%). The elimination of
2-microglobulin in post-dilution is Independent of filter surface area. Pre-dilution removes less
2-microglobulin, than that the post-dilution. Prolactin removed satisfactorily regardless of the filter surface area in post-dilution, and its removal appears to be lower than that of 2-microglobulin.