Is HDx superior to HF- HD and/or HDF?
The list of known clinical advantages of on-line HDF is long and includes better removal of uremic toxins, better control of anemia and mineral metabolism, improvement in fluid overload control, hemodynamic stability and inflammatory status, arterial endothelial function, and left ventricular function, resulting in reduced cardiovascular risk. The anticipated benefit of HDF on the overall survival of HD patients has been observed in several randomized controlled studies, as well as in national registries from France, Australia, and New Zealand (1). Unfortunately, its worldwide spread is limited by logistical, regulatory, and economic investments, since the technique requires an ultrapure water-loop, extra devices, and frequent upkeeping to maintain the quality of water delivered to the patient (5).
The first study comparing the results of HDx with MCO prototype dialyzers with HF and HDF dialyzes was published only three years ago (6). It concluded that MCO dialyzers remove a wide range of middle molecules more effectively than HF-HD, and even exceed the performance of high-volume HDF for large solutes, particularly lambda free light chains. However, even though albumin loss was moderate with MCO, it was greater than with HF-HD and HDF (6). One later study observed no significant difference between HDF and HDx in the removal of urea, creatinine, β2-microglobulin, myoglobin, and albumin (7). Nevertheless, another research showed superior efficiency of HDx in removing larger middle molecules, myoglobin, and prolactin, compared to HDF (8). Similar results were reported by García-Prieto et al, deducing that MCO HD is superior to standard HF-HD in the removal of middle and larger middle molecules and is not inferior to HDF in the clearance of small and larger middle molecules (9). Taken together, these studies reported somewhat conflicting results concerning the efficacy of HDx with MCO membranes in removing beta2-microglobulin, myoglobin, prolactin, and lambda free light chains.
A recently published study proposed a Global Removal Score (GRS) as a new useful tool for measuring dialyzer effectiveness calculated based on the removal rates of urea, beta2-microglobulin, myoglobin, prolactin, alpha1-microglobulin, and alpha1-acid glycoprotein, and albumin (10). The values of GRSs for the evaluated MCO and eight HDF dialyzers are shown in Figure 2. This study reported no significant differences in removal rates of neither of the examined substances with neither of the dialyzers. The dialysate albumin loss was acceptably below 3.5 g in all situations, without significant differences (10).