Utkan Sevuk,1 Erkan Baysal,2 Nurettin Ay,3 Yakup Altas,2 Rojhat Altindag,2 Baris Yaylak,2 Vahhac Alp,3 Ertan Demirtas4 1Department of Cardiovascular Surgery, Diyarbakir Gazi Yasargil Education and Research Hospital, Diyarbakir, 2Department of Cardiology, Diyarbakir Gazi Yasargil Education and Research Hospital, Diyarbakir, 3Department of General Surgery, Diyarbakir Gazi Yasargil Education and Research Hospital, Diyarbakir, 4Department of Cardiovascular Surgery, Liv Hospital, Ankara, Turkey Background: Delirium is common after cardiac surgery and is independently associated with increased morbidity, mortality, prolonged hospital stays, and higher costs. Cobalamin (vitamin B12) deficiency is a common cause of neuropsychiatric symptoms and affects up to 40% of elderly people. The relationship between cobalamin deficiency and the occurrence of delirium after cardiac surgery has not been examined in previous studies. We examined the relationship between cobalamin deficiency and delirium in elderly patients undergoing coronary artery bypass grafting (CABG) surgery.Material and methods: A total of 100 patients with cobalamin deficiency undergoing CABG were enrolled in this retrospective study. Control group comprised 100 patients without cobalamin deficiency undergoing CABG. Patients aged 65 years or over were included. Diagnosis of delirium was made using Intensive Care Delirium Screening Checklist. Delirium severity was measured using the Delirium Rating Scale-revised-98.Results: Patients with cobalamin deficiency had a significantly higher incidence of delirium (42% vs 26%; P=0.017) and higher delirium severity scores (16.5±2.9 vs 15.03±2.48; P=0.034) than patients without cobalamin deficiency. Cobalamin levels were significantly lower in patients with delirium than patients without delirium (P=0.004). Delirium severity score showed a moderate correlation with cobalamin levels (Ρ=-0.27; P=0.024). Logistic regression analysis demonstrated that cobalamin deficiency was independently associated with postoperative delirium (OR 1.93, 95% CI 1.03–3.6, P=0.038).Conclusion: The results of our study suggest that cobalamin deficiency may be associated with increased risk of delirium in patients undergoing CABG. In addition, we found that preoperative cobalamin levels were associated with the severity of delirium. This report highlights the importance of investigation for cobalamin deficiency in patients undergoing cardiac surgery, especially in the elderly. Keywords: cobalamin deficiency, coronary artery bypass grafting, delirium, delirium severity score, elderly