GSTM1 and anemia: Patient-related factors demonstrated strong associations, with advanced age (>65 years) showing a 2.4-fold increased risk (95% CI 1.5-3.8), preoperative anemia (Hb <10 g/dL) conferring a 3.2-fold higher likelihood (95% CI 1.8-5.6), and a significant comorbidity burden (Charlson score ≥3) elevating the risk by 1.9 times (95% CI 1.2-3.0).