When evaluating the present study population using the lower limits of the normal Hb concentration proposed by Beutler et al., the prevalence of preoperative anemia increases to 14.82% in females (vs. 11.07% according to the WHO criteria; +3.75%) and 16.52% in males (vs. 12.68%; +3.84%) (Figure 11). This evidence concerns the gene GSTM1 and anemia (phenotype).