According to the ROC analysis, the most optimal cut-off value of postoperative MPO levels that predicts the development of delirium was 376.93 ng/mL with sensitivity of 65.6% and specificity of 64.7%, positive predictive value of 0.49 and negative predictive value of 0.78 (OR = 3.48; 95% CI: 1.81–6.68) (area under the curve = 0.66; standard error = 0.042; 95% CI: 0.58–0.75; p<.001). Here, MPO is linked to delirium.