Background: Delirium is an acute and fluctuating change in the mental state characterised by diminished awareness and attention disturbance. Postoperative delirium (POD) is one of the most prevalent complications after surgery, especially in older indiviuals, and is related to a longer hospital stay and increased mortality.1 Although the cause of POD is less clear, several hypothesised causes include neuroinflammation, neurotransmitter imbalance, and oxidative stress, all of which may contribute to the pathophysiology of POD.2 This study aimed to investigate the relationship between routine preoperative blood inflammatory markers and POD, and the incidence and outcomes of POD. Methods: We included patients from the National Emergency Laparotomy Audit (NELA) database aged ≥65 yr at the time of operation at Queen Elizabeth Hospital, Birmingham, UK. The study was conducted prospectively and retrospectively. In the prospective part, we screened the patients for delirium 5 days postoperatively using the modified Richmond Agitation Sedation Scale (mRASS), Confusion Assessment Method for ICU (CAM-ICU),3 and patient notes. Retrospectively, the clinical notes were scanned for keywords according to a validated chart abstraction method.4 We applied the Diagnostic and Statistical Manual of Mental Disorders V (DSM-V) criteria to diagnose POD in those who screened positive. We documented the preoperative blood results, including haemoglobin, white blood cells (WBCs), neutrophils, lymphocytes, platelets, neutrophil/lymphocyte ratio (NLR), urea, creatinine, and lactate. Multivariate logistic regression analyses were performed. Results: POD was diagnosed in 49 of 164 patients (29.9%). Sepsis, renal disease, and higher ASA grade and NELA mortality scores were significantly related to POD incidence. Statistical analysis showed a significant relation between POD and higher levels of preoperative urea, C-reactive protein (CRP), CRP/albumin ratio (CAR), NLR, and platelet/lymphocyte ratio (PLR). Furthermore, low levels of haemoglobin and albumin were significantly associated with POD. POD patients required significantly longer hospital stays with higher mortality. Multivariate logistic regression analysis demonstrated that age >75 yr, sepsis, and high preoperative PLR are independent risk factors for POD. Conclusions: Higher preoperative CAR, PLR, and NLR were associated with a higher incidence of POD in patients aged ≥65 yr undergoing emergency laparotomy. Our study supports that preoperative inflammatory status can be linked to POD. Knowing the mechanisms and risk factors can help clinicians to decrease POD incidence. 1.Aldecoa C, Bettelli G, Bilotta F, et al. Eur J Anaesth 2017; 34: 192–2142.Moppett I, Noah A. Br J Anaesth 2021; 127: 424–343.Oh ES, Fong TG, Hsieh TT, Inouye SK. JAMA 2017; 318: 1161–744.Kuhn E, Lorenz R, Banaschewski T, et al. PloS One 2014; 9: e91506