Preoperative serum ferritin as a biomarker for predicting delirium among elderly patients receiving non-cardiac surgery: a retrospective cohort study

Iron metabolism disorder has been identified as a contributor to the pathogenesis and progression of multiple cognitive dysfunction-related diseases, including postoperative delirium. However, the association between preoperative iron reserves and postoperative delirium risk remains elusive. This retrospective cohort study aimed to explore the impact of preoperative serum ferritin levels on the risk of postoperative delirium in elderly patients undergoing non-neurosurgical and non-cardiac procedures. Conducted at the Chinese PLA General Hospital between January 2014 and December 2021, the study finally included 12,841 patients aged 65 years and above. Preoperative serum ferritin levels were assessed within 30 days before surgery, and postoperative delirium occurrence within the first seven days after surgery was determined through medical chart review. The analyses revealed that both low and high levels of serum ferritin were associated with an increased risk of postoperative delirium. Patients in the lowest quintile of serum ferritin exhibited an 81% increased risk, while those in the highest quintile faced a 91% increased risk compared to those in the second quintile. Furthermore, mediation analyses indicated that the direct effect of preoperative serum ferritin on postoperative delirium contradicted its indirect effect mediated by hemoglobin levels. These findings suggest that maintaining serum ferritin within moderate range preoperatively could be beneficial for managing postoperative delirium risk among elderly patients.