Multivariable analysis showed that the Cumulative Illness Rating Scale (odd ratio, OR = 1.89, 95% confidence interval, CI: 1.10–3.25, P = 0.021), preoperative albumin levels (OR = 0.67, 95% CI: 0.48–0.94, P = 0.022), rSO2 at T4 (OR = 0.61, 95% CI: 0.41–0.89, P = 0.010), and postoperative TΔrSO2% (OR = 0.80, 95% CI: 0.66–0.98, P = 0.028) were independently associated with postoperative delirium in older adults undergoing elective abdominal surgery. This evidence concerns the gene ALB and delirium.