GSTM1 and anemia (phenotype): RBC transfusion for anemia only benefits a subset of patients: those with moderate or severe anemia (Hb < 7 gm/dL in several randomized studies) (Hebert et al., 1999; Lacroix et al., 2007), and the early, deficient vasoregulatory capacity of stored blood secondary to depletion of SNO and ATP appears contributory.