Diafilters for predilution and postdilution on-line hemodiafiltration.

When hemodiafiltration (HDF) is performed, we can choose the point on the blood circuit where the substitution fluid goes in, i.e. before the diafilter (predilution) or after the diafilter (postdilution). We must avoid unexpected loss of albumin; however, we should remove a certain amount of albumin in order to remove much larger solutes than β2-microglobulin and obtain better clinical outcomes. Previously, ultrafiltration experiments were performed in vitro using aqueous albumin solution and commercial diafilters. The results showed a high sieving coefficient for albumin right after starting the experiment that is identical to several clinical reports. Based on these results, a novel design of the diafilter was attempted for predilution and postdilution HDF. Diafilters for predilution HDF do not require much change in design specifications, employing hollow fibers with a slightly larger diameter in order to reduce high blood pressure caused by the high blood flow rate. Diafilters for postdilution HDF may require much change, including shortening the length in order to reduce the amount of internal filtration. Diafilters specifically designed for predilution or postdilution may be necessary to assure future success of clinical HDF treatment.