On‐line haemodiafiltration. Remarkable removal of β2‐microglobulin. Long‐term clinical observations

Background. The accumulation of '? 2-microglobulin (β 2 -M) in long-term dialysis patients may lead to dialysis amyloidosis. In this respect, the removal with different modes of on-line haemodiafiltration (HDF) of β 2 -M was studied. Long-term clinical observations in patients with more than 10 years of dialysis, treated mainly with biocompatible and highly permeable membranes and in the last years with on-line HDF are also reported. Methods. In the first part of this report, the reduction ratios and clearances of β 2 -M, blood urea nitrogen, creatinine and phosphorus (P) of on-line HDF with 40 to 120 ml/min replacement fluid are compared with bicarbonate haemodialysis (HD). In the second part, we investigated 16 patients with more than 10 years of dialysis treatment. The prevalence of dialysis amyloidosis and the mean values for serum albumin, serum total cholesterol, HDL and LDL cholesterol and parathyroid hormone are reported, as well as the mean dose of erythropoietin. Results. In the first part with on-line HDF, starting from HDF 60 ml/min a significantly higher β 2 -M reduction ratio and clearance vs HD is noted. In HDF100 (i.e. with 241 replacement volume per 4-h treatment) vs HD, a β 2 -M reduction ratio of 72.7% vs 49.7% (P= 0.0000) and a β 2 -M clearance of 116.8 vs 63.8 ml/min (P=0.0000) was obtained. Comparing HDF120 with HDF100, there is a significantly higher β 2 -M clearance with the former (P < 0.005), although the β 2 -M reduction ratio was not significantly better. In the HDF120 session the amount of β 2 -M in the total dialysate was 292 mg per session. If one adds the known 17% adsorption on the polysulfone membrane, a total of 341.6 mg β 2 -M per session is removed, which adds up to 1024.8 mg a week. Concerning the small molecules, our results with HDF100 also show a higher creatinine and especially P clearance vs HD. In the second part with 16 patients with more than 10 years of dialysis treatment (mean 14 years 1 month), the mean time on HDF amounted to 39.5% of the total treatment time. In four patients only biocompatible and highly permeable membranes were used, AN69 and mainly polysulfone, and in four other patients these membranes were used for more than 95% of the treatment time. Therefore, it is not surprising that the prevalence of carpal tunnel syndrome was only 12.5% in the patients after 10 years of dialysis. Twenty-five percent of these patients met the criteria for diagnosis of β 2 -M bone-amyloidosis, proposed by van Ypersele de Strihou et al., but without a retrospective X-ray analysis. The mean predialysis β 2 -M value was 29.6 mg/l. The mean values for serum albumin, serum total cholesterol, HDL and LDL cholesterol were within normal limits. For the parathyroid hormone a mean of 287.5 pg/ml was found. Subtotal parathyroidectomy was performed in five patients. The mean dose of 43 U erythropoietin/kg per session is comparable with those reported in the literature. Conclusions. Like Canaud, in our renal unit, treatment with on-line HDF with a highly permeable and biocompatible membrane has proven to be an efficient, well-tolerated and safe technique. Furthermore it leads to a low prevalence of dialysis amyloidosis and a superior P clearance. However, continuous attention must be paid to an on-line sterile and apyrogenic dialysate. Although on-line HDF is undoubtedly a more optimal approach of chronic dialytic treatment, it also carries a higher cost, which is currently evaluated to be nearly US$11 per session.