Our results showed that high preoperative composite risk index, a combination of frailty (mFI ≥0.27), malnutrition, moderate to severe anemia (hemoglobin < 90 g/L), and severe hypoalbuminemia (albumin ≤30 g/L), was independently associated with an increased risk of in-hospital POCs in older patients undergoing elective digestive tract surgery. This evidence concerns the gene ALB and anemia (phenotype).