The independent variables (age, sex, weight, Hb, Ht, anemia, coagulopathy, duration of surgery and the six surgical specialties) influenced 27.5% of the variance in the use of RBCs (Hosmer and Lemeshow p=0.55; Omnibus Test of model, p<0.001). The gene discussed is GSTM1; the disease is anemia (phenotype).