Evaluation of dialysis outcomes: experimental versus observational evidence

Evidence-based medicine provides tools to evaluate dialysis outcomes by integrating knowledge obtained from interventional and observational studies. This is illustrated in relation to three important topics: dialysis membranes, dialysis dose and anemia. Clinical trials and observational evidence support each other in indicating a decrease in dialysis-related amyloidosis morbidity when high-flux dialysis is used, whereas the impact of dialysis membranes on mortality is still controversial. Two clinical trials are currently investigating this issue: the American Hemodialysis (HEMO) Study and the European Membrane Permeability and ESRD Patient Outcome (MPO) Study. As indicated by the National Cooperative Dialysis Study (NCDS), dialysis dose is an important determinant of patient outcome. Although Gotch's analysis of the NCDS showed no further benefits for Kt/V>0.9, the analysis by Keshaviah showed a progressive benefit as Kt/V increased beyond 0.9. This finding has been confirmed by observational studies, of which the Dialysis Outcome and Practice Patterns Study (DOPPS) is the most recent and interesting. Further information is also expected from the HEMO study. The findings of observational and interventional studies are consistent in indicating anemia as a major determinant of morbidity and mortality in dialysis patients. American and European guidelines advise hemoglobin levels of 11-12 g/dl and hematocrit levels of 33-36%. The real benefit of completely correcting anemia is not so clear. In conclusion, far from being in opposition, clinical trials and observational studies can provide an integrated contribution to the analysis of dialysis outcomes.