The use of SDS–PAGE scanning of spent dialysate to assess uraemic toxin removal by dialysis

Background. Uraemic toxins in the 8 to 60 kDa molecular weight range have been attracting increasing attention in dialysis therapy. However, there are no available standardized methods to evaluate their removal. Using new filtering membranes, we evaluated SDS–PAGE of spent dialysate to assess cut-off ranges and removal capacities into dialysate, while also measuring classical markers of dialyser function. Methods. Eighteen dialysis patients were washed out for 2 weeks with FX 100 (Helixone®), followed by randomization to Xevonta Hi 23 (Amembris®) or FX dialysers for 2 weeks, then crossed over for an additional 2 weeks, and finally placed on Xenium 210 (Purema®) for 2 weeks. SDS–PAGE scanning of the removed proteins contained in the spent dialysate was performed during all dialysis sessions. Total mass of urea, creatinine, total proteins, beta 2 microglobulin (β2m), retinol-binding protein (RBP) and albumin were measured. The reduction rates of serum urea, creatinine, β2m, leptin, RBP, alpha 1-antitrypsin, albumin and total proteins were also determined. Results. SDS–PAGE scanning identified four major protein peaks (10–18, 20–22.5, 23–30 and 60–80 kDa molecular weight) and showed clear differences in the amounts of removed proteins between the dialysers, particularly in the 20–22.5, 23–30 and 60–80 kDa ranges. Total mass of removed β2m, RBP and albumin were in agreement with SDS–PAGE, while serum assays showed differing results. Conclusions. SDS–PAGE scanning provided a good characterization of protein patterns in the spent dialysate; it extended and agreed with protein determinations and allowed a better assessment of dialyser performance in removing 10 to 80 kDa molecular weight substances. It also identified differences between the three mainly filtrating polysulfone dialysers that were not detected with blood measurements.