GSTM1 and anemia (phenotype): However, patients carrying the CC allele in the non-Spx group were more susceptible to anemia than those carrying the CA/AA allele (Hb decline of 1.74 g/dl vs 0.60 g/dl, P < 0.05), whereas there was no difference in Hb decline between patients carrying each genotype in the Spx group (0.96 g/dl vs 1.28 g/dl, P = 0.89, Figure 2B).