GSTM1 and anemia (phenotype): Recent studies have evaluated the risk factors for anemia and blood transfusion: a low preoperative Hb level, higher blood loss during surgery, longer operative time, higher ASA score, the use of surgical drains, female gender, older age, higher BMI, comorbidities like Chronic Obstructive Pulmonary Disease (COPD) and bleeding disorders, black race, and steroid use [13].