GSTM1 and hydrops fetalis: However, although the Red-HF (Reduction of Events by Darbepoetin Alfa in Heart Failure) study, a large-scale clinical study of ESAs in patients with cardiorenal anemia syndrome, showed improvement in hemoglobin (Hb) in the ESA group, the primary endpoint (all-cause death or re-admission because of worsening of heart failure) was not significantly different from the placebo group.