Dual-threshold plasma Aβ oligomerization for postoperative delirium risk stratification

BACKGROUND: Postoperative delirium is common in older surgical patients, but simple blood tests to identify risk are lacking. Plasma amyloid-β oligomers measured by multimer detection (MDS-OAβ) may reflect neurodegenerative vulnerability. METHODS: We enrolled 101 patients aged ≥65 years undergoing elective orthopaedic surgery with general anaesthesia. Blood was drawn preoperatively and at first delirium diagnosis or on postoperative Day 4 if no delirium. MDS-OAβ was quantified blinded. Delirium was assessed daily on postoperative Days 1-3 (DRS-R-98 and DSM). Propensity-score matching on APOE ε4 status and clinical covariates addressed Alzheimer-type vulnerability. Discrimination and thresholds (0.60, 0.72, 0.85 ng/ml) were evaluated using logistic regression and ROC analyses. RESULTS: Among 101 patients (44 with delirium; 57 without), preoperative MDS-OAβ concentrations were higher in those who developed delirium and correlated with delirium severity. In the overall cohort, preoperative MDS-OAβ discriminated delirium with an area under the curve of 0.855 (95% CI 0.777-0.919); in a pooled postoperative dataset (n = 205), discrimination was similar (AUC 0.884, 95% CI 0.837-0.925). The dual-threshold approach identified a low-risk group with high negative predictive value and a high-risk group with high positive predictive value, leaving an intermediate group for closer observation. CONCLUSIONS: Preoperative plasma MDS-OAβ may provide a scalable biomarker for perioperative risk stratification of postoperative delirium in older adults, supporting a dual-threshold strategy for targeted prevention and monitoring. Low MDS-OAβ values indicate lower risk but do not exclude POD; biomarker-guided stratification should complement, not replace, routine perioperative delirium surveillance.