Understanding associations of hemodialysis practices with clinical and patient-reported outcomes: examples from the DOPPS

Due to the scarcity of randomized clinical trials (RCTs) in nephrology [1], particularly in dialysis, there has been uncertainty about optimal practices. Using standardized data collection, the Dialysis Outcomes and Practice Patterns Study (DOPPS) has shown very large betweenand within-country differences in hemodialysis (HD) practices and patient outcomes. These observational data are especially useful in areas where results from clinical trials are not yet available or where a randomized design may not be feasible, e.g. for ethical reasons or high cost. Observational studies have influenced medical treatments for many decades, but can result in biased and misleading findings if appropriate statistical methodology is not applied, since treatments are often confounded by clinical indication. For example, we observe that HD patients treated with erythropoietin have lower—not higher—post-treatment hemoglobin levels than patients not treated with this agent because the indication for therapy is a low hemoglobin level [2]. In the DOPPS, a vast amount of information on potential confounders, as well as application of sophisticated statistical techniques, contributes to improve comparability among treatment groups with the intent to yield more robust results. In the following sections, we review selected studies from the DOPPS that have clinical implications for practice at the dialysis facility, and we provide some comments about the reasons for the analytical approaches used.