While Goodnough et al1 provide a recent review of selected anemia management and mortality studies, their conclusions regarding the end-stage renal disease population must distinguish between association and causal effect. As noted by Goodnough et al,1 cause-and-effect relationships are difficult to prove using observational retrospective analyses. Although the observational studies cited in their Commentary may suggest that anemia is "an independent factor impacting mortality," bias due to confounding may be present.2 In other words, there are a multitude of other reasons that may cause both the anemia and increased mortality (eg, chronic inflammatory condition).3 In this case, anemia is an innocent bystander, and ameliorating the anemia will not necessarily impact mortality.
Cotter D. Does the Evidence for Anemia Treatment Support a Survival Benefit?. Arch Intern Med. 2003;163(19):2395-2396. doi:10.1001/archinte.163.19.2395-a