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The type of dialysis membrane used for routine therapy has been recently shown to correlate with the survival of chronic hemodialysis patients. We examined whether this effect of dialysis membrane could be explained by differences in dialyzer removal of middle molecules using data from the 1991 Case Mix Adequacy Study of the United States Renal Data System. The sample analyzed included patients who had been treated by hemodialysis for 1 year or more, who were dialyzed with the 19 most commonly used dialyzers in 1991, and for whom delivered urea Kt/V could be calculated from predialysis and postdialysis blood urea nitrogen concentrations. Vitamin B12 (1,355 daltons) was used as a marker for middle molecules, and the clearance of vitamin B12 was estimated based on in vitro data. After adjustments for case mix, comorbidities, and urea Kt/V, the relative risk of mortality for a 10% higher calculated total cleared volume of vitamin B12 was 0.953 (P < 0.0001 v 1.000). Similar results were obtained when middle molecule removal was adjusted for body size. We conclude that both small and middle molecule removal indices appear to be independently associated with the risk of mortality in chronic hemodialysis patients. Differences in mortality when using different types of dialysis membrane may be explained by differences in middle molecule removal.

There is an ongoing discussion in the renal community about how to monitor the treatment of hemodialysis patients in the United States. Comparison of the US patient experience to that of other countries with populations of similar heath status is one way to assess treatment. Another technique involves examining the level of dialysis therapy US patients receive. This paper reviews recent studies which found that the United States has higher mortality than both Japan and Europe and provides additional information as to why those comparisons might be underestimating the mortality differences. We also examine the data on the level of dialysis US patients receive, both as a prescription and as delivered care. We conclude that US patients receive less hemodialysis therapy than their European and Japanese counterparts, and that in general US patients are not receiving the level of dialysis they were prescribed. These factors are correlated with an increased mortality among US hemodialysis patients.