GSTM1 and anemia (phenotype): <h4>Background</h4>Preoperative anemia is common and associated with adverse postoperative outcomes.<h4>Objective</h4>To evaluate the association between preoperative anemia severity and clinical outcomes in patients undergoing elective noncardiac surgery.<h4>Methods</h4>This retrospective cohort included 23,579 adults assessed preoperatively between January 2015 and August 2025, all with documented hemoglobin (Hb) and hospitalized for noncardiac surgery.